thank you for the help I will check the exhaust flap, we did have it changed under warranty some time ago.What did you do last August?
(tires, perhaps? Brakes?)
and I ask somewhat out of the cost effectiveness. from 41 to 38 mpg over 20,000 miles would mean a difference of 40 gallons.
487 up to 526 gallons
so spending more that what you think 40 gallons of diesel would cost might not be cost effective.
I do not track my mpg so closely, but see that yours is not too far outside the range of other golfs. not the best, but not the worst.
last paragraph has hints on how to run adaptation/test of exhaust flap.
worth a shot.