thanks for the replies..
I have erred in thinking that the bmw warranty has to be continuous.. Does anyone know if porsche has to be continuous as well?
In any case, my c63 covers about 5,000 miles annually. I bought it 18 months ago at 18000 miles and now it has 26,000 miles. I would rather build up a piggy bank for any repairs than fork out for a warranty. The only thing i am worried about is the drivetrain (ie engine and transmission) but since the cost is close to £1200 annually, it seems that i am better off just putting it off and probably factoring into the price once resale comes around. The car will only be serviced by MB anyway.
I think the same goes for my bmw z4m... 12000 miles, 5y old car.
still if i were using the car as a daily driver, I'd probably consider taking WD because of the substantial savings.