Parts Geek, as well as Europartssd have been good for me. Ive just bought a few sensors(IAT, MAf, water in fuel) from partsgeek, all of which were either genuine mb or bosch. They're prices are better than europartssd, but they don't give you much info on what you're buying other than part #s, so you have to do some research on what youre buying. I had to double check part #s with the sensors I was replacing. The sensors branded "Standard" seem to be genuine mbenz. I don't think there is any number to call with tech questions. Europarts spells stuff out for you on their website and you can call and talk to a knowledgeable person if you have questions, which can save you time and money in the end.