Mexico City is not as dangerous as everybody thinks. It is so large, you don´t notice any drug cartels activities unless you go to specific districts. Southern part of the city is nice and quiet. The worst that can happen to you is get your pockets picked on the subway.
You can register on the local forum, where there are vendors that can help you get the parts you need for your car, and a bunch of guys in the city and surroundings that do ocassional meetings.