Interesting.
When I lived in the Dominican Republic we had an automobile that ran on Autogas (LPG) and we always filled our portable tanks for Camping at the GAZ station.
Never had a problem. Never noticed any oil either.
Could it be a country specific thing?
Only thing I can think to do is put an inline filter in.
AS for your theory about Winnebago putting oil in. I doubt it is a usual practice.
YOUR location states Japan. If you PM me I would be happy to contact Winnebago for you and see what they say. With the time difference it might be a PIA for you to try.
Let me know
