Repair or replace Kohler shower handle/valve?

I just moved into a 9 year old house and the shower in the master bath has a slow leak (drips at the shower head, not handle). It's a single handle (turn) style shower handle/valve by Kohler. I've taken it apart and replaced the rubber O-rings which looked a bit worn. I neglected to note the model #'s of the parts. It has a large brass valve-body and a plastic cased valve/cartridge which is where I suspect the slow leak is. It is a shower-only model, no bath.

With a fixture that is 9 years old, is it possible to find replacement valve cartridges? If not, do I have any other options besides having a plumber tear into the wall to replace the entire valve body along with a new handle?

This may seem like a stupid question, but I work in Pediatrics and not home repairs. Any help/advice would be appreciated.

Yes, you should be able to rebuild the valve. Kohler seems to have a build of the day, though, and you need to get the right parts to do it; unlike Delta and some of the others that have used the same guts for numerous years. From what I understand, you'll probably have to go to a plumbing supply house and order the parts. Best thing is to probably take them with you. This can be a pain, as often you have to shut the house water off because there are no individual shutoffs in the shower. I've been told that the parts catalog for Kohler is more like a telephone book.