Yes, once moisture/dirt gets in, it will start corroding the piston

 

you can get a replacement kit on Rockauto and they are easy to replace

 

wow - all that rust corrosion on the caliper piston housing - I could tell your vehicle lived in the "salt zone" w/o even looking at your profile... I am always amazed to see the undercarriage of any car that resides in the northern states compared to the sunny and mostly "salt free" southern states. Big - huge differences... Whenever I have shopped for a used vehicle I immediately cross off any vehicle that the car history report shows was in the North.

 

I went OEM two years ago, and installed. I removed the pistons completely before install to do a clean job. (I don't recall if removal was necessary.) The hardest part was deciding, if I wanted to pinch-off the brake hose line to keep the fluid from running out. Pinching-off worked fine for me. But, I suppose some brake lines could crack.

 

An aftermarket caliper rebuild kit is about $4 usd plus shipping off rockauto. Or use a genuine toyota kit and change out the pin dust boots too. use only a JIS K2228 approved grease like CRC Silaramic, or Toyota pink brake lube on the pins.

For caliper rebuild I just use brake fluid and no pink grease. Use a rubber plug to plug the brake hose banjo. I personally don't like to clamp reinforced hoses.

 

Mine was torn also. I found out over time that dirt and debris was entering my caliper through that tear in the rubber boot. When I went to bleed the brake, the fluid was very dirty. You can rebuild it, the seal kits are not that expensive. It just takes time. You might need a rubber plug like JohnGD had mentioned to plug the steel brake line so you don't lose all your brake fluid while you are working. Rebuilding the caliper is fairly easy. It isn't rocket science, it just takes time. Another really good option is to get a rebuilt caliper from RockAuto. Since the Highlander is a very popular SUV, there are plenty of decent reman calipers out there. I would recommend replacing the rubber brake hose at the same time.

 

I was able to find a caliper from a written off Highlander. I also purchased the rebuild kit. I have never done caliper build just wanted to give that a try. As of rust my highlander is not too bad but my 01 Solara rusted out badly. I am going to retire that car next year. So sad engine and tranny is in great shape. Thank you all for responds.

 

I replaced the single-piston front calipers on my other vehicle with a compatible dual-piston calipers, which were rebuilt with an OEM kit. Saw a few YT videos on how to get the pistons out and was able to use a small compressor to push 2 of 4 out, while the other two had to be pried out. The kit had everything essential to rebuild the calipers, while some other parts weren't used. When the piston wasn't coming out, I kept applying small amount of brake fluid wherever possible and used a brake caliper press tool to push the piston back in, after some back-and-forth actions, the piston finally popped out. Other than that, the rebuilding process isn't too bad, spray the dissembled calipers with some brake cleaner, lubricate all the parts, and put everything back. I struggled with the first clip trying to secure the boot over the piston since I didn't want to tear the boot, but eventually got it in and rest of the 3 were pretty easy afterwards.

 

Yes, will corrode and freeze piston or drag caliper. Just found the same on mine and replaced them from Rockauto. Was super cheap for boot kit. LIke 5 bucks for front and 3 for back.