Old Walker drive loses torque

I have an old 1988 commercial Walker MC36 with the 6.7 grass catcher that I have semi-retired to personal use on my small lawn. When I pull the mower out of the shed everything seems to run fine, but as the mower warms up the right drive motor loses torque. After about 30min I have to stop mowing because there is zero pull remaining on the right side. Is there anything I can do to repair the existing drive? Our local Walker shop says $750 for a new drive. I hate to spend that much on a mower I use so little, but I also can't buy a mower of this caliber for that money. Hoping for a miracle to keep this one running. Thanks in advance for your help.

https://www.google.com/search?sourc...r mower part 5025&aqs=chrome..69i57.17889j0j8
take at look at prices on these sites.

https://www.google.com/search?sourc...walker mc36 parts&aqs=chrome..69i57.11876j0j8

Not knowing your skill level but have you thought of rebuilding it. From what I have heard you take it apart and change the o rings and put it back together. Like $40 dollars in parts.