That last bolt was stubborn. So I cut it off using a Dremel and cutting wheels. First I had to wait for the battery to charge, then I went through 3 cutting wheels. With that the draw bar came right off the trailer hitch. I cleaned it up a little and took it to the welder. I thought I would be dropping it off and picking it up next week, but he took it right away and about 10 minutes later the new receiver tube was welded nicely to the draw bar...only cost $20.
Back at home I used a wire wheel to clean up the draw bar and welds, then primed and painted with a couple of coats of black RustOleum ($4). Before I could remount the drawbar I cleaned up all the bolts and nuts with a wire wheel and lubricated the nuts with PB Blaster. When they were sufficiently clean I could run them most of the way up the bolts just by hand. Then, I had to remove the remainder of the bolt that I had cut off. It required more cutting to make it shorter, then it slipped out of the hole.
I decided that 3 bolts out of 4 will be sufficient for the time being. So I remounted the draw bar with the 3 bolts. Some time in the future I will probably get 4 new bolts. It was amazing how many tools were needed to use to get this job done. I cleaned them all up and put them away.
The hitch looks and works great now. I can mount anything without the spare tire interfering. And my back feels perfectly fine now too! Total cost was about $45, compared to buying a new hitch for about $170 plus shipping.