I have no scientific basis for my suggestion but I will tell you what I would try first if it was my coach. Instead of filling the gas tank I would put in 5 to 10 gallons of fresh gas with a pint of SeaFoam. Add the recommended amount of Seafoam to the oil and when the 10 gallons of gas is almost all gone, change the gas filter, oil and oil filter. Good Luck.
Jan and Rocky
Volunteers for USFWS. 29 refuges with 9300 hrs ea since 2006. 2004 Allegro 30DA, Workhorse 8.1, Banks, 2012 Jeep Liberty Jet, Blue Ox Aladdin, Brake Buddy Advantage Select, 300 watts solar, 5 Optima group 31 AGM's, 2000watt Ames PSW inverter.