I found an interesting study on propane vs. lubricating oils .This time a (large one) piston-compressor was concerned.
http://docs.lib.purdue.edu/cgi/viewc...8&context=icec
This story is worth reading when judging/evaluating the importance of superheating/subcooling/the meaning/necessity of extra HEX between evaporator and compressor in terms of R290 (this far).
No corresponding scientific stories available rgd. mini splits (this far)!