The brass part on the original ones spin freely( poor design) The heat from the hot water side has made the glue holding the brass loose. This happened on two showers.

Pics show what I have. I've tried a couple extensions I got from homedepot. One was to long ( the sleeve could not reach the threads)

The other looked to be perfect but it was to wide in diameter. It would go into the sleeve but there is a step at the end of the sleeve that it would bump into. I could thread the sleeve in a tighten but there was to much friction and the knobs would need too much force to turn.

So I'm looking for the proper stem extension. Might replace the stem too. Getting a nicer looking sleeve would be good if anyone knows a replacement.

This has been very frustrating. Yesterday I bought the ones that were too long. I tried all day trying to rig those up to work by cutting them down. Thought I was good to go but only to turn water back on and find them leaking. Today I went and bought the ones that looked to be the right size and still no go.

So any help is much appreciated.