Inspect the roller bearings and make sure you have enough in there and that they are all circular and without flatspots. There shouldn't be room to fit one more bearing but they should be relatively loose fitting. McLube won't necesarily hurt them but they should work with out it (in this case, lubricating the bearings - like traveler cars - can cause the bearings to slide rather than roll leaving flat spots on the bearings which leads to more sliding and less rolling. Sloppy bearings, like in traveler cars and cattrax, need a little friction to make them roll properly.

It may just be that you have grit up in them - I would disassemble the whole thing, clean it with water, and reassemble...it's a simple system and if something is wrong, it should be pretty obvious.