The manufacturers warranty on a BMW is 4yrs or 50,000 miles but if you are are trying to discern between the bmw m3 extended warranties then this should help.  An extended warranty by design should extend the coverage of major mechanical and operational parts on your bmw and lessen the financial cost of having to fix these parts as they wear down.

Extended warranties also make it more affordable to continue taking your vehicle to the dealership where you have the best chance of a A.S.E certified mechanic or technician working on your vehicle and using OEM replacement parts for the repairs.

Extended warranties can be purchased from the dealership at the time you purchase your new or used vehicle or you can buy a policy through an outside company later on after the purchase. Typically it may cost a little more if you go with the later option but it is available to you.

A warranty on your BMW M3 can extend as far out as a 100,000 miles and there are some policies that can be bought for mileage above a 100K.  Regardless of the policy you should look for the extended warranty to cover the Engine, Automatic/Manual Transmission, Front Suspension, Rear Suspension, Steering, Brakes, ABS Brake System, Electrical, Air Conditioning/Heating System, Cooling System, Interior/Exterior, Fuel System, Final Drive Assembly and Propeller Shaft. The more of these things that the warranty covers the better it is.