Yes, the pistons are the "sliding/moving" part that ride against the seal. They need to be smooth. Rock Auto may have some, I ordered some a while back.
I just bought 8 New Pistons and 2 Seal Kits From RockAuto. Once I popped out the Frozen Pistons out of the calipers it seems that I actually could have tried to clean a few up and reuse them, but since 8 new ones were available I bought them!
