A mechanic replaced the rack and pinion on my 1997 Volvo 960. After getting it back, it immediately starts to leak power steering fluid. I could get by by constantly refilling the reservoir. I took it back to get fixed and they said it needs a new rack and pinion; the replacement was "faulty" but was under warranty. This was 6 or so months ago. The part came from Rock Auto and so they are handling the replacement, but one hasn't become available. I finally log on and see that there is a rack and pinion available on Rock Auto for the 1997 Volvo 960, but it is a TRW design and the mechanic says I need the CAM design one, which is still out of stock. I am close to buying one anew somewhere else, but why can I not use the TRW design?