I would make sure that the engine is running Ok and able to come up to full power. Look into the hydraulic tank to see if anything is abnormal. I'm not sure, but I think that the oil filter is installed in the pump suction side of the reservoir,10W-40 engine oil is used in the hydraulic system. I did have to replace the hose from the oil filter to pumps on a 260K for a local cemetery. These machines have very durable hydraulic system components, pumps and wheel motors.
If you would like manuals, send me a PM with your email address and I can attach the parts for the 260K and the operators for 251K/260K machines.
They are not as difficult to replace v belts on as they appear, but you need OEM belts particularly the double V belt.
Mad Mackie in CT