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The reason for leaking, most times is that something has gone leaky
Some thoughts : too much oil in the gear, gear has gone too hot, too much working hours, mounting failure of manufacturer.
Advice would be change the gearbox.
We have two robots. KR 500 R2830
Life time robot 1 - 16300 hours
Life time robot 2 - 16441 hours
Both of them leak at the same time.