Hi Peter.

From all the ideas that came up on this thread, it looks as the real problem is flood-back and oil wash out.

A suction line accumulator will add some protection to the compressor.

a coalescing oil separator should solve the problem of the oil.

I would check all the refrigerant control components in the system for perfect operation and the electrical controls and timers for the right operation sequence.

I dont think adding some other refrigerant to help oil return would help to save the compressor in this case.

Chemi