It was just leaking a little

I just rebuilt these 20 years ago. You would think sitting in the garage for the last 6 they would be in better shape. Lols. I was hoping the pistons were in better shape but no. Master cylinder bore cleaned up well. I flushed and blew out the lines and splitter best i could. I don't even want to think about the rear right now.

Yup, brake fluid is hydroscopic. It sucks moisture right out of the air. That is the main reason it is supposed to be changed every other year.

So the caliper bodies cleaned up fairly well. I'm finding out the pistons are nowhere to be found on the face of the planet. There's some in the UK I saw but I have issues with them. Has anybody tried them? Anyways, I guess my choices are do I put it all back together and hope it works? Or do I get a new set of pads to push back the pistons beyond where the pitting meets the seal? Any thoughts on the piston pitting?

Those pistons will probably tear the seals !! who is the UK supplier ? a lot of the US guys speak highly of "Brakecrafters"
What bike are they for ?

   Search on 'phenolic caliper pistons'.   We've been seeing chatter about them for a few years.  There are some for vintage Honda and Yamaha.  We've also seen a few for some vintage Kaws.   Haven't yet found any to fit our Z1's.  You may be able to match needed OD's from another caliper.  Minor variations in length may not be an issue.

Good Ridin'
slmjim & Z1BEBE

Brakecrafters seems to have them.  Be sure to replace your brake lines if it hasn't been done in a while.  The inside of the line is filled with the same scum as the caliper.

And I've had bad experiences with K&L brake caliper seals over the years.  They are commonly too tight, and won't allow the piston to move freely.  Hope you don't have the same issues.  OEM is much better.

I need caliper pistons foe the 1100. I haven't had the 750 for maybe 10 years.
   Update. I do remember the 750 having the same set up as the 1100. Thank you for reminding me.  I did some triple checking and will be calling them shortly.