Well, here is my story. When I went to rebuild mine, I just went to a local store. I was in a hurry. I got the part, but the cylinder was too big. Maybe just a mm, but the bitch wouldn't fit. I tried a yet another chain thinking it was just a mistake, but I got the same problem. At this point I called up the dealer, gave them my vin number and ordered the rebuild kit.
I thought for sure I had it. Nope, too big. On the mitsu part, the stocker piston in green and I got a pink one that was just a tad too big to fit in the stock slave. Well, I had to fix my leaky problem cause this car was used to get to work. No backup. I just ordered a whole new one. When I did, it came with the pink cylinder.
I have no ideal why no one (even Mitsu) could not match the stock piston on a rebuild kit. It's only maybe 1, 1.5mm bigger, but when you are tring to rebuild the slave with a bigger piston, it seems a lot bigger.
To this day, I don't know why there is a green (smaller piston) and a pink (bigger piston) for the slave cylinders or why even the dealer with the VIN couldn't get the right part to me.
I can only guess that the stocker is NLA.