If you already have an "approved" German car. Take it to "Schwarz Liga A".
Win the three races there and win a beautiful new M3 Racecar.
Failing that keep an eye on the used car lots, buy the M-coupe, change the oil, lighten it, slap in the race tranny, and flywheel. Maybe some minor HP increase.
Then run it in the "M" manufacturer's races. Win, and walk away with a nice new M3 GTR.