MightyMouse only scrolling in one direction (AFTER complete disassembly + cleaning!)

I've completely disassembled and cleaned not one but two Mighty Mouse's (not so mighty IMO) and while the rollers were quite dirty, it seems the problem is more software than hardware.

The ball scrolls up, left and right but not down. So then I went to the Mouse preference pane (in 10.7.5) and changed the option of 'scroll in the direction the ball rolls' i.e. inverted or not inverted scrolling. Low and behold now it scrolls left, right and DOWN but not up. I've heard it might be something to do with Lion but IDK.

Anyone have this problem? (or the solution?) TIA

Advice: Toss the "Mighty Mouse" in the garbage and buy a real mouse that works. It took my brand new "Mighty Mouse" just several months before the ball got so dirty it had to be disassembled in order to be cleaned. They're a real pain and not worth fooling with. Buy a Magic Mouse or Magic Trackpad if you like Apple rodents, otherwise do like I do and buy a $12 Logitech Optical mouse in Walmart which seem to last forever.