I'm on such a high right now, after 4 days of trying to beat this final mission, I made it.
The main trouble is the suspension - really springy - and passing the cars in front, because the 'Ring's road is narrower than a normal racetrack, it's almost like driving Monaco with no room for error.
I drove much more aggressively on this lap than the previous 4 days, almost drifting corners by applying the brakes lightly forcing the car to turn into the corner with the end kicking out. Passed the 300 SL on the penultimate corner and spent a lot of time punching the air after finishing the lap with a 2 second lead. The credit prize and the bonus car makes it extra sweet.
Having a rest now for a few minutes, driving with the DFP in a racing seat has actually caused me to lose a smidge of weight over the past 4 days because I've been driving the 'Ring so intensely and it's been really hot here, and I've ended up a tad exhausted.
But yeah, it's nigh on impossible that race. Good luck chaps!
Suze