the suspension is reliable. weakneses are the air spring units at the front. little stones dust and grit get trapped inbetween the boot and the metal inner bit, eventually holeing the bag. think the're about £240 each???? very easy to fit!
you'll know it when it happens, cus you'll park it up and when you come back to it a couple of hours later it'll be on the slant. then when you start it up the suspension warning light flashes while the pump trys to restore the ride height.
to give you an idea.... i work at an independant vag in sheffield. ive fitted probably 8-10 of the front bags in the last 5 years.... out of probably 15 - 20 allroads that visit the garage.
not fitted any rear bags... ever.
the valve block can go faulty too, changed 2 in the same sort time period.