yeah bb that was one of my thoughts too but these linde's drive everything through the hydraulic system, drive, hydraulics, steering and in some cases even the cooling fan.
If contaminated fluid from a failing pump was the case he should be seeing fluid leaks from several sources, not just the one.

I'm thinking some sort of pressure issue.
He should have the pressures checked and make sure they are withing machine specs. If it's high this could cause this. That would be the first thing to check anyway on these machines.