Okay, I got it fixed. I went to the stealership and they had the fitting for $4.95. The only problem was that they had to have it shipped from Milwaukee and it was gonna take three days to get here (Friday.) So I went back to Auto Zone and pulled the fitting. It turns out they had one that matched the threads in the block and ALMOST matched the threads on the sensor (the sensor has a tapered screw and the elbow I used was straight-bore, but the actual threads were the same.) It was serviceable enough and only cost $1.99 so I just used that. I used teflon tape on both the fitting and the sensor so I don't think they'll be able to work their way out. The most expensive part of this was paying $19.99 for a five-quart jug of oil to refill it with.
After test driving for a while she seems to be running fine. The only problem I've noticed is that now when I floor it I can hear the valves rattling. When the fitting cracked I did drive the Jeep for a few hundred feet with 0 oil pressure and I could hear the engine knocking (had to do it to get it off the street) so this worries me a little.
BTW the fitting is 1/8" NPT.
