but this is what I just bought and used to replace the o-rings. It worked really well, and seems to be built ok. I'm sure there are better ones on the web, but most are still as pricey.
http://cgi.ebay.com/ebaymotors/Mercedes-Diesel-Injection-Pump-Socket-Engine-Parts-Tool_W0QQcmdZViewItemQQcategoryZ35625QQihZ002QQitemZ120195137730
Also I don't know if it fits your engine.