I think there are settings you can change. Sounds like this is the "report" showing fuel consumption. There is a different option to choose that shows tank level.
This looks like the most likely culprit. I have read that using Noflex Digester can clean the tank and all the associated parts. I bet a few tanks of Noflex would get this type of float system working again.
You are talking about a gas strut. I got one for my 290 at west marine. I agree it should have been original equipment. Measure how far the door moves to find the size you need.
