If the purchase price is worth the car in parts and she drives as well as you say. I'd get it and run
Auto Rx through it for as long as needed. (Before all the wrench heads get their panties in knot and start flaming snake oil, take a look around the net first),
Bobistheoilguy forum is the first place to go, here also
http://www.auto-rx.com/rms13/ The BMW guy tried Auto Rx but did not follow instructions and did not run it long enough.