Rear PBR rebuild kit question

[Saber]

So im in the process of installing my new rebuild kits i just got, and besides a few of the usual troubles i seem to always have i have one quick question. The kit came with a balck circular ring, im assuming its an o ring of some sort, in the directions it shows this going in the piston bore part of the caliper, however, when taking my current ones apart, i never came across this part in question, it says the rebuild kit is for 91-92 third gens 93 and up camaros and i believe the c4 vette. Do i have to use this? even though i never had on before? It also makes it pretty hard to get the bottom dust boot to seal up in the piston bore when putting everything together, and i dont want to force the issue if im not supposed to have it.

[ebmiller88]

Have you taken your piston out yet? If not, it's still in there. You must have this piston installed or the caliper will leak.

Ed