Er, um, I was just doing a dollar conversion there. If the rear left is rattling in the Boxster you wish to purchase and it's diagnosed as a bad strut, you should ask the existing owner to replace them before you buy the car. It an expensive repair in my recent (two weeks ago) experience...
1. Can't replace just one — replacing both rear struts is important for your suspension so you don't go bouncing around with one new one and one old one. $350.00 + s/h if you buy them off a web site as I did. Bilstein heavy duty struts are what I bought (not the sport model, which are more $$ and provide a stiffer ride).
2. Labor to install them is about 3-5 hours, and part of the job requires two people if I am not mistaken. My mechanic only charged me $300.00, his rate being $75 an hour. My local stealership is now $98 an hour, but they quote and charge off a spec sheet from PCA, so it doesn't matter if the mechanic is fast... you pay the same, and it will be more than I paid. Call the Honolulu Porsche service dept. and ask what labor only is on rear struts.
3. A four wheel alignment is required after the rear struts have been replaced because it knocks the whole rear end out of alignment. I paid $78 + tax for a four wheel laser alignment that gave me a four page color printout. Firestone has the same equipment and will give a lifetime four wheel alignment for $120.00... I'm doing it with them next time.
Not to discourage you, but rear strut replacement, if indeed that is the source of the rattling, is going to cost you upwards of $750 or more.
Now it might just be a LOOSE Strut bolt... that's a five minute fix by most any mechanic... and I do hope that's all it is. When I bought my boxster I had a rattle at low speeds and found out it was a broken weld on the exhaust. Five minutes in a muffler shop to spot weld it back and no more rattle. Sometimes, fixes are cheap, but "cheap" has not been a word I've used often when discussing repairs on our cars.
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