just read this post and wanted to say, This is not a bad issue at all and is easily fixed. like the guys have mentioned before, they are tight and in some cases some fit actually tighter than others.. A small jewelers file is what I use in this case and (file) the inside flats of the gear.. Do Not file the aluminum drive end.. ( if you ever replace the gear again after a crash, it may end up Too Loose.. Do this until you get a nice light dragging feel when you engage the gear onto the shaft. Also a very common issue that will arise if you force these gears on when you assemble and install the tail it will actually push the mushroom gear into the beveled gear and cause binding.. The gear mesh should be absolutley Butter Smooth when rotating it.. If this infact happens you will need to reset the gear and this can be done when everything is assembled however if you don't do it correctly and the gear is actually (to tight of a fit) on the TT, you can damage the gear itself... Hope this helps some..
K