Anyone familiar with Champion D720 transmission problems after long-term storage?

[George]

I recently bought a 1977 Champion D720 grader with a DRMCO9138 transmission that sat for nearly 20 years. The engine runs and I've primed the clutch, but the machine won't move. I'm only getting small traces of transmission fluid at the lines and wondering if I'm dealing with low fluid, a charge pump issue, stuck valves, or loss of hydraulic pressure from sitting so long.

 

[MasterBuilder15]

After sitting for 20 years, I'd see things first..verify the fluid level, replace all filters, and check whether the charge pump is actually building pressure. Long-term storage can leave valves stuck with varnish and seals dried out, so a pressure test might tell you a lot before tearing into the transmission.