After using I separate the reels into two pieces, rinse both out thoroughly in warm running water then leave the pieces to air-dry. I've never had trouble with buckling, with either 35mm or 120 film. I think what's important here is to keep guck from building up on the little balls. I bought the reels new and always cleaned them this way.
Also important is to make sure the reels are correctly loaded. If you feel any resistance at all, pull out the film carefully and re-load. The film has to advance smoothly and easily right up to the end.
I've always found steel reels difficult to load properly, but that's just me.