14 y/o car that's been through who knows how many owners - I wouldn't bet that they've been maintained properly. I doubt it would pull either way though, as long as you clean up the sliders on the other one and re-lube them, it will be fine.
I most enthusiastically agree about not trying to repair the caliper. Even if you don't care that it's going to totally screw over the next guy when he wants to get new brake lines - there's no way you're not gonna get chips in the hole from drilling and tapping the new thread. That means you need to pull the caliper apart completely anyways which means new seals, and a good cleaning, getting all the rust off, and now it's become too much of a pain. Just get a new caliper.