Onan oil filter threads damaged

S.O.P. for filter installation is hand tight and usually 3/4 turn further after contact and still by hand. The same for removal,although in practice removal frequently requires a boost from a filter wrench and then removal by hand. Coming off hard all the way with tools required is really out of the ordinary. I have to wonder if you got ahold of a filter with a different thread pitch. Maybe a metric thread being applied to a u.s.s. thread or vice versa. Many techs might not recognize any difference and just force the issue. Apparently worked ok until removal time came. You are getting good advice here and I would follow their lead and order the proper parts from Cummins. Check this also. Many cummins/onan filters will cross over to Kohler numbers and again vice/ versa. As well their may be some of each that look alike and have different threads. This is one reason it is so important when purchasing parts and accessories that serial and model numbers be provided.