I finally got the parts, tools & time to look at it today. The drive belt was sort of the problem.
The hydraulic pump is driven by one belt from the engine to the top of the rear axle assembly. The rear axle assem. is mounted to the frame with 2 bolts on either side, bolts go through the axle housing and a flange off the frame. There's also a cross-brace just forward of the axle housing, two bolts go through it and into the axle housing.
When the heads break off the two cross-brace bolts the housing will try to rotate either up or down depending on which direction you're traveling. If you're going forward, the front of the housing rotates up, which applies more pressure on the belt driving the pump. If you're reversing, the front of the housing rotates down, loosening the pressure on the belt, allowing it to slip and stop driving the pump, which explains the loss of reverse.
This back & forth rotation also causes a *lot* of stress on the two mounting plates on the sides. That stress then causes both plates to bend
and crack.
I hope to have all the bending, welding & bolt removal/replacement completed tomorrow. I'm also adding a few pieces of 1 1/2" angle to reinforce the mounts. While I'm at it, I'll be looking to see if the cross-brace/bolt can't be strengthened somehow.
I'll go ahead and replace the belt while it's apart....
I do like the new jack. I got the 350# unit:
https://www.amazon.com/gp/product/B06XTD5Y9X/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 It's pretty lightweight, and the wheels are useless on anything other than a smooth concrete floor, but it lifts my mower just fine, it'll make changing the blades and cleaning the deck a lot easier.