leaky shower faucet - help needed

[bowersba]

LazyPup and others give some great advice here - I hope you can help me, too.

My shower faucet first was not regulating water temp correctly and now leaks badly. It is the type with a single round control know that slides up to turn the water on and turns left/right for hot/cold. It has the ball inside with the holes in it. The pipe has the two rubber o-ring thingies with springs in them - I think that is where the problem is although I cleaned everything and don't see anything wrong with them or any other parts. Home was built in 1977 and this is likely the original plumbing.

Please help me fix this. Is there a "better" system I can install w/o having to change any piping?

Thanks!!!