Or malfunction in a way that would make the car sort of "twitch" when driving? When moving the wheel side to side, nothing appears abnormal. But when simply driving, sometimes the steering angle will actually change, almost as if I had a "loose" alignment and my front wheels were literally moving. ALignment is fine, it's been checked three times. The shop says they are 99% sure it's the rack, but I want to be dead sure this is a possibility (not that I don't trust the shop, I just can't afford to spend money on repairs that aren't totally necessary.)

 

if you are driving say on a bumpy road and let go of the steering wheel and it moves by itself unpredictably then yes, this usually means your steering rack is wearing out. there is really nothing else that can cause this problem except for bad alignment, uneven tire wear or loose lug nuts but you seemed to have checked that already. also have the inner tie rods checked, if both sides are worn, it could cause the steering to twitch.

 

This happen to me! exactly how your describing it. Had about 95000 miles on my mini. It turned out to be the rack and pinion and was brought back to new after about 800 bucks.
really hurt to pay it but i cant explain how happy i was when i got my mini cooper handling back! lol

 

Different manufacturers use "pot metal" for the steering racks or other mechanisms. You can read more here: http://en.wikipedia.org/wiki/Pot_metal. It appears the under-dash is pot metal, but I may be wrong.

The shaft that went from the key to the actual ignition switch in the steering column of my old '85 SS Monte Carlo broke once. It was made of pot metal. I took the opportunity to rewire it with a starter switch.

 

I've seen a couple racks that had too much play in them. And even seen one that the case broke when the guy drove off the road.

I have a good used Steering rack if you need to save some $$

 

PM'd.