RE: fr5-300 oil vs fr7-420
Bax,
Thanks. Not something I am going to experiment with.
I always pump some red ATF in through the breather and turn it over, and plug the breather, before putting away after flying.
As for OS knowing what they are doing...talk to FS120SP owners with failed regulators and no solution even when they were current models, or seemingly hiding the solution to failed regulator covers on FS120-P Surpass engines. We only found the solution to this last problem by knowing somebody who worked at the importer, and gave us the part no for the modified cover.
jp