Water is leaking to floor beneath upstairs shower below tub only when shower is in use. Diverter is not working properly. Removed diverter stem, can't really see any water damage around plumbing stems. Is it possible this bad diverter or stem can leak water inside wall as it is only when shower is in use? Thanks for any help

The mixing valve, diverter, pipe up to the shower arm can all leak like you describe. Start by removing the handle and the escutcheon plate so you can get a better look. Ypou may need a small mirror to look up along the pipe to the shower arm. Watch for traces of crusty water deposits.

Thanks for your response ballengerb1. I've got the diverter stem out which is from an eljer three stem system from the 60's. I noticed the cover for what I believe is called the trip lever drain system in the tub is a different brand. Perhaps this cover and gasket that looked suspiciously worn, wet, and not properly fit, could be leaking water behind the tub. Between the leaky diverter running water near or over it and the stream of a couple showers, I hope trying to replace and see if this works. We just bought house that was built in 1968 and are discovering all these wonderful plumbing issues.

I would suggest replacing the entire valve if you have the skillls to solder