I had 91,000 miles. Replaced the rails just because of age - 1988 vehicle. After the install including new tensioner, zero stretch.

It took me about 7 or 8 hours to do eveyrthing, but it was done a hour or two here and there over a week and a half. Did top 3 rails, cam oilers, all belts and resealed the rear cover of the p/s pump.

Pin puller - just to a yahoo search on "mercedes pin puller"

$65 - looks the best

http://www.etoolcart.com/browseproducts/Mercedes-Benz-Rail-Pin-Puller-Guide-M0044.HTML

$35 - It will work fine, but mught require you find a few
sockets, large washers or pieces of pipe to make it work.

http://www.etoolcart.com/index.asp?PageAction=VIEWPROD&ProdID=160

The real benifit to these tools is that they allow you to put a 14 or 15 mm wrench on the bis nuts to pull the pin out. I was using a 6mm x 45mm cap screw with a stack of large and small washers. Not fast or efficient. I would spend the $35 in a second if I had to do it again.