Rack and pinion question
 

I have a question for y'all. I have a '99 A8 4.2 Quattro, and I'm at least in need of a new rack and pinion for it at least on the driver's side. I don't really want to replace the whole assembly because that would obviously cost more money. The rack is leaking fluid almost immediately after I put it in. My question is if I get the one component, can I get away with doing that instead of the whole assembly? On eBay I found two of those rack and pinions, part number 551-58784. My mechanic gave me the part number for the whole assembly, and that is 3B1422052L. Any possibility that that would work? Please let me know, thank you! If not I'll take any advice that you may have! The leak is right near the boot by the way.