I finally got the plugs out. My friend finally got around to welding my bolt and nut together. (I took a 14mm wrench down to the Bolt Bin and asked for a bolt with a 9/16 or 14 mm hex head. I think the bolt size was 5/16. Bought a number 8 grade 1-inch bolt and a couple of nuts.) He left a 1/10 inch or so gap between the bolt head and nut, then filled the gap with weld along the middle of each flat side, leaving the corners sharp. In spite of soaking with the catalytic stuff and rapping the plug with a hammer, then repeating a week or two later I still had to grunt with a long breaker bar. The fill plug was really tough. To get past the exhaust pipe using a socket I had to use a 6 inch extension, which I braced using a jackstand as a fulcrum.
Interesting, but probably not worth saving $15 or $20.
The old gear oil looked like molasses, and a fair amount of metal shavings were in the white plastic drain pan after I poured it into a waste bottle. So much for dealer maintenance--I bet it was the original oil. Also, I specifically asked the dealer to change ALL fluids when I bought the vehicle used.