Replace or reuse, 38mm stainless early rear caliper piston
 

Replace?http://forums.pelicanparts.com/uploa...1745875408.jpg


http://forums.pelicanparts.com/uploa...1745875425.jpg

that looks like a chrome plated piston to me, not stainless.

Perhaps, although I don't see an option for that on our host site

You have it apart so just put a new one in.

Hi
The original OEM pistons are chrome plated steel and prone to rusting..
The replacement non OEM ones these days are often made from stainless steel, removing the rusting problem.
If you choose to replace, probably best to replace both pistons in the caliper.
Cheers

These little guys were such a pain to remove. The air compressor barely moved one side.

I bought a cheap $77 Chinese Vervor diesel pressure tester and mated up a 12mm connection (to a rubber hose i found on a Mercedes repair site) to the caliper. I fixed the diesel leaks by applying a few wraps of plummer's tape to the inside nipples (cleaning the holes for flow) after connections I ran a small wire to clear any incidental Plummer tape blockages. No leaks!

Since the pitting is at the very end would that come in contact with the square round rubber ring?

I would use it. The corrosion on the end might only come in contact with the seal when the pads and rotors are brand new even then likely not or just barely.

That is before the seal. Just shine it up to remove the rust.

I've just done mine and they were similar. Clean it well and grey scotchbrite the pistons. It'll be fine.

As long as they don't come in contact with the rubber I think I'll reuse these.
Thanks all