Look inside your bdrm closet door. There is normally a list of all appliances with model numbers. Most toilets require they be removed to replace that gasket, however one new model (not mine) can be repaired in place. The kit will include a base gasket if you need to remove the toilet.
Online or RV dealer....
You tube video gave details when I changed mine.
My 2011 sprinter with 310 toilet replaces thru the bowl. no removal.
2011 Keystone Sprinter 323BHS. Retired Master Electrician. All Motor Homes are RV's. All RV's are not Motor Homes.