On our 07 Magna, the Fuel Gauge was 'Not accurate!'. We were told to clean the top of the Fuel Tank's Fuel Gauge Sending Unit, which I did with lots of Simple Green, then after drying - followed up with unscrewing and cleaning each of the wire leads into the Sending Unit. (I even removed, one screw at a time, and used Emery Cloth to clean the connections.) It did not solve the 'less then accurate' Fuel Gauge reporting.
So I asked Premier RV Service to check it out, and the Tech confirmed a faulty Sending Unit. He use a 5 gallon bucket, and properly calibrated a new Sending Unit, then installed this unit - and we're probably within 5-10% accurate reading (I believe, more accurate towards the middle of the tank, then at the top or bottom range.). We typically live on the top 3/6th of the tank, rarely dropping down to 1/3rd of a tank...
Sure would not hurt to do a deep cleaning of the surface area at the top of the fuel tank's 'Sending Unit'. IF you do so, pull the 12V fuse before cleaning...
Wish you the best of luck on this,
07 Country Coach Magna Rembrandt 45' ISX600
Roo II was our 04 Country Coach Allure 40'
OnDRoad for The JRNY! Enjoy life...