The problem is with the starter drive gear . the gear is made of a plastic/fiber material and the drive parts wear with use, then "bind up" in the flywheel-blower wheel teeth. when you reach in the air intake end and grab the flywheel fins you can usually break it free by turning it in opposite direction of normal rotation. the only fix is to replace the starter, which usually requires pulling the genset from the RV, as the enclosure cover has to be removed to access starter. There are really cheap starters available on-line, but they are really "cheap"! You get what you pay for...I would go with ONAN part; 191-2351, usually available for under $100 from Onan parts dealer.
