1985 225 Cat excavator 51U 3208 motor

Just recently got this excavator. Worked fine then stopped swing and travelling left track without warning.
Fluid level is good. It makes no attempt to swing or travel left track. No change in motor while trying to swing or travel. Right track travels fine, main boom operates fine,
dipper not fully operational.
Any suggestions where to start looking for problem?

1985 225 Cat excavator 51U 3208 motor