I have changed others in my house, but not this one, so don't think it
is soldered. No others have been soldered. I think it is just tight
and old. Luckily it is right outsid of my garage, so the lead pipe is
not too difficult to access if there are signs of a leak. I have
drywall there, but it isn't finished.

Isn't there some type of chemical I can use to loosen the tension?