Bought new Transmission/gear box.
Putting in the new one was easy. Taking the old one out was a nightmare. The corrosion on the spanner nut and drive block was awful. Ten years of VERY hard water and six kids made for a lot of corrosion and hard water crystallization.
I do not own a spanner wrench. I am not sure having one would've helped. I tried pipe wrenches, needle nose vice-grips and many other ways. What eventually worked was taking a three inch ratchet extension, putting it against one of the notches on the spanner nut and pounding with the side of a carpenter hammer. I also used lots of penetrating oil and let it soak for about 48 hours.
I then had to figure out how to force the old shaft and the drive block out. When it should have been free to move, it didn't. We pounded so hard that we bent the metal where the feet screw in. Eventually, I decided that we were going to have to buy a new machine. Once that decision was made I could be more violent in my pounding. I supported the bottom of the tub on blocks of wood (Two 6X6 stacked on each other) so there would be room for the gear box to fall out. I took a steel barbell put one end on top of the shaft and smacked the other end with a five pound sledge.
It took a lot of effort. But, it worked! Amazingly, the plastic bottom of the tub did not crack. I scrapped and scrubbed as much gunk off the parts as I could.
Putting it all back together wasn't bad at all. Very easy. It works great! It is quiet. It doesn't leak, and works again as if it was new.