Norma, It’s important to run the engine at least monthly. But just as important is to let it run long enough to heat the oil to proper operating temp. (see temp. gauge). This burns off any condensation & out gunky stuff from the oil. Also , apply the E brake and step on the regular brake at the same time. Run through the gears to lube the transmission also. Don’t rev the engine or let the RV move . Hold each gear (D,R,N,1,2,3) about 4 seconds each.
Hope this helps