I have an older house with a dripping shower nozzle. The control trim is labeled Moen Dialcet. I've taken off the clear acrylic single control handle searching for either a washer or cartridge to replace but see neither -- no retaining clip, nothing. Brass & plastic parts are also very mineral stained and Brasso & CLR have only minimally made them look better. The valve is behind tile and the back side is not accessible. Any ideas or where to find parts/and or fix the thing? I've tried Ace Hardware & Home Depot.