One belt drives both pumps? And you say unit is sealed, no reservoir? Is it possible that the weak one is not cooling properly? Loose fan on hub perhaps? Have heard of that. Another idea is that the weak one is covered with crud, making it heat up more than the other one. I have heard of that happening, and sometimes can be due to oil leak in one of the two hydro units, or other source of oil getting on just one pump. Have you washed the pumps with solvent and rinsed them both off? Good thing to do at beginning of cutting season. Ditto for hydromotors, but much more mporttat for hydro pumps. Can you drain and refill with higher viscosity oil? Don't know if anything available in thicker stuff tho. Never have investigated.
