The only thing I can think of that happens quite often from experience working on them is the window regulators. Especially the front ones. We dont run DRL's down here in the US, at least not on those older ones, so not sure about that. the other stuff is probably mostly due to age more than it being a problem area per se.
As for the heater, my 94 will roast you out of the car. Put it on all the way hot and set the fan at the low setting on fresh air and in 15 minutes you will be stripping your clothes off. I know it is a different engine but I would guess the heater core and things like taht would be the same. Have you checked to make sure the hoses going to the heater core are not collapsed or anything like that. Also the valve that opens to allow water into the heater core, make sure it is operating correctly.
As for the heater, my 94 will roast you out of the car. Put it on all the way hot and set the fan at the low setting on fresh air and in 15 minutes you will be stripping your clothes off. I know it is a different engine but I would guess the heater core and things like taht would be the same. Have you checked to make sure the hoses going to the heater core are not collapsed or anything like that. Also the valve that opens to allow water into the heater core, make sure it is operating correctly.