I have a tire valve (on '94 YJ w/ stock & standard rims) that leaks at
the stem base until I put a little lateral pressure on it (and the
leak stays stopped if I shim it that way). My guess is given location
at base of stem it's the stem, and not the valve itself.

Is my understanding correct that it's easy to replace the valve itself
w/o tire removal, but to replace a leaking stem you have to remove the
wheel, break a bead seal on the tire, insert new stem from inside the
rim, then rebead the tire and inflate? (In which case I guess I'll
spring for the $20 shop repair as much as I like taking 4 hours to get
the frustrating gratification of doing it myself.)