I have fans on LOTR, WOZ, Metallica, AFM, Tron and the lower right flipper on TSPP. All of these games experience slightly weaker flippers over long games... convection simply isn't enough to draw sufficient heat off the coils during long, intense games. I want these games to play as snappy on the 10000th flip as they do the 1st, and fans help greatly towards that goal. The flippers could still make all shots without the fans, but this helps keep action consistent throughout the game (and day).

Also check to be sure the plunger is not angled at all as it goes into the plunger - the clamp on the flipper bat must be properly aligned vertically so there is minimal friction as the plunger is drawn into the coil.