you will need one for the m42. The early 318's had the m10. There are quite a few chips out there for you to choose from. The "best" is the markD chip according to most people. Thats going to run you above $200 new. The cheap route is the ebay chip. Thats a road that seems to be pretty controverial [spl?]. I personally have one in my car since it came on the car when I bought it. But I also have the stock chip and I deff like the ebay chip over the stock one. I will be installing MS soon so I will have that up for sale sometime.
Hope that helps some