Yes, moisture, starsan and unrinsed PBW will all cause the bung to slip freely out of the carboy to varying degrees. I wipe the neck and bung down with a rag soaked in starsan and wrung out to nearly dry to dry them off.
I'd like to throw more support behind the "no sugar" necessary camp.
I have done 4 cheap juice ciders and 3 fresh pressed ciders. The ciders I added sugar to have tasted worse (IMHO) generally. My ice cider, which was almost all FCAJ maybe 25% juice and is strong AF, tastes like ass. It's been sitting in the back of my fridge for like 2 months since I tasted it last though.
So far cheap juice with US-05 and yeast nutrient, fermented @ ~68 has been my favorite batch. Really refreshing and easy drinking. The fresh pressed 4 apple cider-blend juice I got from Rev Nat is a close second though. Really complex flavor there, but I think the Nottingham flavor is coming through a bit too much. A taste reminiscent of dried wheat perhaps? Is this what they call 'barnyard' in the tasting guidelines?