honestly, i always do cups and seals but i believe the cups SHOULD be ok. the reason, the labor is the same and the parts are cheap. propane is a good idea. you could have an intake seak leak and all the injectors in the world won't fix that. but, i have a smoke machine. use a long hose and go slow. found a couple of misses in bmws around the rear engine seal with propane. good luck, chuck.