i just picked up a 93 fxdwg 1340 cc stock motor...i want to change all the fluids..it has 27650 miles,i forgot to ask what oil he used in her..will it hurt anything if i put amsoil in it..even if he used another brand.i have heard stories that bye changing oil could soften up the gaskets...is that true..or can i put amsoil20w50 syn.in it and be alright