I'm currently going through "Bud" Fortier's book while he was a pilot in the USAAF in WWII, and from his accounts the missions where none had to turn back at some point because of some malfunction in their P47 or P51 (not even combat related) seem to be the minority. Of course, he reports mostly on the missions where something interesting happened... like someone having to go back at some point, even though the rest was a "milk run".
I already suck at Il2... this is going to make me suck even more! I can barely wait