Let me get this straight... the mechanic felt it was the rack.... SOMEWHERE along the line, the rack didn't get changed but the pump and associated items DID (I'm sure there's a story in there somewhere)....
Interestingly, it was "after a while" that it got so bad that you had to take it to a shop....
Here's what I'm thinking... the rack started "going south".... It got ignored long enough to take the pump with it.... The pump got changed but the rack was so full of crap that, eventually, it took out the new pump..... Bottom line, the rack is still bad (bad racks don't usually "jerk" but often exhibit "morning sickness").
Moral of the story... if something is busted, it will remain busted (since it can't heal itself).... If it stays busted long enough, it can bust other stuff.... Keeping on top of repairs as they are required usually has it's long term rewards... delaying repairs, most often, has a way of increasing the size of the final bill....
Important things to remember.... a good tech is merely a communicator... he listens to your car - translates the information into English - converts that to a dollar amount and tells you.... There is no requirement to shoot the messenger.... You don't tell the doctor how to cure you... you don't have the experience or knowledge. Unlike the human body (relatively unchanged for how many eons?), the automobile is in a constant state of flux.... Imagine how a doctor would work if, every three years, your kidneys, liver, heart, brain and sphincter swapped locations and/or started functioning "differently". You wont believe a mechanic who is looking at your face.... how could you believe someone that could be messaging on "I heart clean little boys" (for all anyone knows) all the while he is browsing a newsgroup... how could you believe someone that could tell you it is the interocetor gone bad when we all know that the flux capacitor is out of alignment with the flam ring???? (I just had to add that).
Forrest Gump once said something - didn't have a damned thing to do with a box of chocolates - that his momma always said.... I'll spare the gory details...