Have you turned the key only to see idiot lights come on and no sound from the starter but sound from the solenoid? Does your starter work only when the car's been parked for a few hours?
Before you get a new starter, consider implementing this fix...essentially, the ignition switch and (in my case) 31-year-old wiring are trying to carry the entire current to the starter. This wire is probably pretty narrow-gauge...maybe 12. When conductors heat up, their resistance increases...meaning that the battery can't punt enough amps through to spin the starter.
Putting a simple relay in the circuit can make all the difference to a starter that's 'heat soaked'. My car used to need an hour or so before it would restart, then I got the OBX headers (and a starter blanket) and that time climbed to an hour and a half...then two hours...then two and a half hours...until it just wouldn't start at ALL. So I wound up fixing it in the parking lot of Walmart, in Texas summer, 95 degrees, sunlight, 90% humidity, borrowing a jack and stands from the service department. Don't be like me...IF YOUR CAR DOES THIS FIX IT BEFORE IT GETS WORSE because it will and you may not be stranded near a 24-hour Walmart.
Standard 12V automotive relay. Can be four pole, you don't need five-pole. Suggested 30 amp capacity.
~4-5 feet of heavy-gauge wire--10 gauge is good, 8 gauge may be overkill. If you can't find heavy gauge wire or are stranded at your local Walmart, check the extension cord / power bar department. Most stores sell dryer cords, which are either three-phase or four-phase, have 10-gauge wire, really thick insulation, and one end of each wire comes pre-crimped to some handy terminals.
A couple feet of 12-gauge wire...you could probably get away with 14 or even 16 but if you're going to rewire ancient DC, why screw around?
Wire terminals; I used 5x insulated female spade connectors, 1x insulated male spade connector, 1x butt splice, and 2x ring terminals.
Inline fuse holder...25, 30 amps, whatever you think the starter is supposed to take.
Wire cutters, strippers, and crimpers. The nicer the better, the sharper the better.
Jack / jackstands or hydraulic lift. You CAN do this with a flattened box as a creeper with the car on the ground but you can only get one hand up to the area and it makes everything take about ten times as long and if you have the undertray still attached it may be impossible.
Test light--optional, but strongly recommended.
Note: Steps denoted by (a) are for doing this the RIGHT way. Steps denoted by (b) are for doing this the EASY way. (b) works, it's just not quite as clean, but it takes a lot less time and you get a lot less heat stroke if you can't get access to do (a). If you're paying somebody else to do this, be aware that (a) may also incur additional labor costs.
1) Jack the car up. Safely now.
2) Locate where you're going to mount the relay in the engine bay.
3(a) Remove the connection at the starter. Harder than it sounds. Replace it with some sort of terminal crimped onto a length of your heavy-gauge wire, then crimp a female spade connector onto the other end of this length of wire. Make sure the female spade connector end will reach the relay and the wire takes a safe path (don't route it against the exhaust manifold or you've undone the idea already).
3(b) Leave the connection at the starter alone and follow the wire back into the wire loom. With any luck the wire you're following doesn't go up to another relay. This wire loom on a TE72 will come down by the oil pan, which makes a great place to tap into it. It's a black wire with a white stripe (again, on a TE72) which you will want to make about quadruply sure is the right one. Cut the wire. Crimp a connector (recommended) or splice (if you can find one that will fit both 12/14 gauge and 8/10 gauge securely!) onto the end going to the starter as firmly as you can. Feed an appropriate length of heavy-gauge wire from your relay's mounting position down to the first connector/splice. Crimp the opposite connector onto this length and join the connectors, or put the length into the splice and crimp it shut.
4) Attach the heavy-gauge wire's female terminal end to pin 87 on the relay. There should now be a beefy wire from 87 to either the starter itself (a) or the last couple feet (b) of original wiring.
5(a) Splice enough wire onto the former starter wire to reach the relay, and splice a female terminal on.
5(b) Splice enough wire onto the OTHER END of the cut wire to reach the relay and splice a female terminal on.
6) Connect this female terminal to either pin 85 or 86 of the relay.
7) Connect whichever pin you didn't use in (6) to either the negative terminal of the battery directly or to a solid frame ground via a crimped female terminal and a ring terminal (or whatever's appropriate for your application). I unscrewed the body ground screw and put my ring terminal over it. You don't have to use heavy-gauge wire here, 12 or even 14 is OK as long as 12V can flow across the relay from 85 to 86 or vice versa.
8) Crimp & terminal as appropriate to run heavy-gauge wire from the positive terminal of the battery to pin 30 of the relay. This is where you want to put your fuse holder. I wound up disassembling the positive battery terminal and putting the ring terminal of a section of dryer cord onto it. This is your power feed, make it count and be careful. Rubbing could lead to fires/etc.
9) Double-check your connections. Pin 87 should be the output to the starter (or last foot of starter wire), pin 30 should be the input from the battery. Pins 85 and 86 should be the original starter wire and a connection to (-) or ground. If you have a pin 87A it should be unused...that would be an output that was live whenever the starter WASN'T being cranked.
10) Try it! If your wiring was skinny and aging before this relay, then the cranking and starting ought to be much quicker now. If you took the (b) approach, consider applying a layer of electrical tape and re-looming your splice before you drop the car back down. Let me tell you it is a LOAD of fun when a splice comes loose, then a connection comes loose, and the speed bump getting out of the apartments knocks it back off every time you leave the complex...and crawling underneath the car with a cardboard creeper while an assistant cranks it once you push things back together is great for theft prevention but really, really sucks otherwise.
There is a kit from Larry Buck over at http://www.startercontacts.com/relay.htm
for something like $27 before shipping, he includes the relay, wire, good instructions, terminals, and a connector for the relay to sit in....unfortunately all his supplied wiring is 12-gauge. If you want to go that route be aware that I had an issue where the wires weren't completely secured in the connector, that could be for any number of reasons but I wound up using a bare relay zip-tied to a bracket.