Forget what I said yesterday about DIY: today, I feel like a mechanical frikkin' genius.
Still stewing over the fact that only six of the eight trailer-hitch bolts were properly in place, I resolved today to take another crack at it. Driving home from Target this hot-steamy afternoon, I had a ridiculous idea: I'd put some bolts in the freezer to shrink them. Then I'd take them out to the sun-baked metal of the car and see if I could make things fit.
Success seemed highly unlikely -- yesterday, the threads wouldn't catch at all. Still, if I ever had any plan to tow anything, I'd have to get those remaining bolts in place. So I gave it a shot.
And it worked. It worked so well, I almost couldn't believe it was my idea. Now all eight bolts are in at 75 foot-lbs., and we are ready to haul ass.