1) Do the Boxer Spirit in Professional Hall to get the RUF "Yellow Bird".
2) Use this on Schwazwald Liga B to get the 1992 Mercedes Touring Car.
3) Use this in Legend of Silver Arrow (Mercedes one-make event) to get the AMG Touring Car.
4) Take this for a spin on the DTM Championship and get the CLK Touring Car worth some 700,000 credits.
Rinse, wash and repeat step number 4.
And don't do B-spec, some of the races are really good (like the RUF/Schwarzwald B Races). If you want a challenge, skip step 3 and enter the DTMs with the 1992 Mercedes Touring Car for 110-135 points per race.