So I recently acquired a pair of R56 calipers to upgrade my R53. They came off a car being parted out, that I know nothing about. They’re dirty and have a bit of superficial rust, which is not a big deal, I plan on cleaning them up and painting them.

What I can’t decide is if I should rebuild them or not. Right now the pistons are fully retracted, so I have no idea what they look like, but the dust boots look like they’re in decent shape from what I can tell. I’ve never rebuilt calipers before, but it doesn’t seem too complicated. Is it worth putting a new seal and dust boot on them before I put them on the car? Or should I just throw them on the car and see how they feel?

 

Daily driver...yea, I would.
The rebuild kits are cheap (an o-ring or square ring and a dust boot each). The action of doing the rebuild is just a few minutes of removing any old garbage, grease, leaked fluid. Give everything a good bath after scraping out the old stuff. Lube the new seals with brake fluid, and put them back together. Don't forget to use fresh gaskets.washers at the brake line attachment point.
Should take no more than an hour or so for doing both.

Mike