Twice I have lost the oil, 80W, first time due
to a vent tank for expansion, the second time the output shaft seal fell out
due to the aluminum case expanding faster that the seal, resulting in a fire

Seals in aluminum housings must be positively retained. A silicone "O" at the base of a seal cavity allows oil retention at high oil temps. A seal for the seal you could say.

 

A similar problem is found in racing transmission tail-shaft seals and differential housing seals.  

 

Here are some methods.

 

Lynn E. Hanover