peterh337 - hopefully nobody would get a nasty shock by being threatened with a (big) bill. All I was advocating was for people to check with their CAMO (or your LAA Inspector if your aircraft is on that system) before switching to UL91: it prevents people getting it wrong - which does happen. And sadly there are some unscrupulous people out there who might be slightly less pragmatic about the actions to be taken if someone accidentally used UL91 in an unapproved engine. It's a good idea to double check, is all I'm saying.
As to different oils: I concur with others - there are plenty of alternatives and no, I don't work for Shell!