Excavator house creeps clockwise only with the bucket loaded up high

Roughly 9,400 hours on the clock. Load the bucket and lift it up and the upper carriage walks clockwise about a degree a second with the joystick sat dead centre. Empty it out and park and it will hold position all day without a twitch.

So far I have changed the swing brake solenoid and checked pilot pressure - 42 bar at the test port, right where the manual says it should be. My next move is dropping the swing motor to inspect the crossover reliefs, but that is half a day gone on a hunch.

Has anybody run this one down before? Is there a quicker test I am overlooking?