So, my problem might be very simple, but it's confusing. After a few hours of work, the swing gearbox case fills up with oil, and it starts coming out through the breather cap. Okay, I understand that the swing motor seal is worn out—classic. But the confusing part is that when I checked the next day to see if the swing case was still full, the oil level was just slightly above the high mark on the dipstick. How is it possible that the excess oil disappears? All i can think of is that case is cracked and oil leak out or hydraulic system *somehow* sucks excess oil out. None of these are credible
The extra oil in the swing transmission may have created enough pressure to damage the seal on the pinion/ output shaft. Check the swing gear, there shouldn't be oil in that compartment.