Tips for fixing tight waist swivels?

I recently bought Combiner Wars Deluxe Swindle, and while the toy is great in every mode I've found that the waist swivel is stiff, so much so that it's hard to move without popping off one of the ball joints in the hips. The only time I've really had issue with this is when I have Swindle in Combiner arm mode, it's hard to pose because of the tight swivel. Can anyone suggest a way to fix the waist swivel so it moves more smoothly?