Mine is the same as Peter's, factory standard slope and no mods to rubbers. Drains could happen if ball comes slow from the bumpers but a few nudges at the right time will bounce the ball off the standard rubber ring and avoid the guts.
I find the worst drains happen if you do not clear either of the two ramps or if you bounce the wrong way off hell's bell.
AC/DC plays like all Ritchie machines of old. You need to give 100% and maintain the smooth flow. Once you start loosing control of the ball you will get many drains; SR pinballs are not for beginners, they are challenging and adictive. On a slack day, I will struggle to crack 30m. but when SR says "you're on fire!", I frequently crack 150m.