Delta shower lever ball questions..
I don't know about other people, but we never caulk our shower trim. Shouldn't really need to with that seal on the back of the plate IMO, unless you plan on spraying it directly with a fire hose, it probably won't leak. It wouldn't hurt to replace that little foam with some decent weatherstripping I guess since you have it apart.
As far as the ball, i've not had extensive experience replacing those yet, but so far, the ones that i've done were dummy-proof, IE : there is only one way that they will go into the valve.
did you compare the ball with the old one to make sure it's exactly the same?
other than that, if you didn't tweak anything else, i don't know.