I have just encountered a problem in an older house (built approx. 1978) concerning a leaking shower head. There are both cold and hot water valves below the shower head. For both the valves, ALL that is protruding from the surface of the tile is about 11/16" of what looks like 5/8" dia. threaded (steel?) pipe nipple. From the middle of each of the two nipples protrudes about 3/8" of a 5/16" dia. fluted brass piece for knob attachment (threaded hole in the middle of the brass part). There are no retaining rings and the threaded nipples are completely grouted in to the the surrounding tile.

Does anyone recognize the brand of valve? Not being familiar with this type of valve, am I going to have to remove the grout around the nipples, deep sockets to remove and replace what I assume is some type of cartridge? What is correct procedure? Thanks.