It may be something easily repaired, but I suspect that you will have to open up the wall to repair it. Start by taking the handle off and the round wall plate off if it has one. Look into the hole. There should be a plastic piece that is round where the assembly comes through. What do you see? Is there any cracks or breaks in it? It you want to take it apart turn off water first then do the above. You will then remove a brass clip in the back of the assembly, this will allow you to take the "guts" of the assembly out. That is where you will find the washers and all.
cholbach@yahoo.com, June 2005