the mylar caps will have a stripe on the body indicating which end has the foil on the outside. this should be connected to the ground side of the circuit (except in a voltage multiplier where only 1 or 2 ground points exist and the rest of the caps are floating). the reason for this is to keep the cap from re-radiating noise, not for any "polarity" reasons, as mylar caps don't have anything resembling polarization. you may want to look through the scope for any more paper caps like that, and replace them all. i have an antique radio i rebuilt as a teenager, and i'd replace one paper cap, only to have another one fail soon afterwards (the first cap to fail protected the rest of them from failure by shorting first). i finally sat down with the schematic, figured out where all of the paper caps were, and replaced all of them with mylars. that's where i learned about the outside foil marking, as the schematic specifically said that the outside foil of the cap should be the ground end.