The Tesla LDU (Large Drive Unit) used in certain Teslas, including my P90D has a flaw with the cooling system. There is a seal that will eventually fail with a 100% failure rate. When the seal fails, coolant leaks past the seal, washing grease out of the bearings and damaging the stator and eventually the inverter. Given there is no weep hole in the LDU, there is no external evidence that the seal has failed. Here are some links for more information:
Early MS LDU/RDU coolant leakage; current state of affairs
DIY Tesla Drive Unit Repair