Is it where the arch liner rubs on the chassis member just above the driveshaft, or on the wing?
If the former, I would sand it back and cover the patch with 'Greystripe' from Halfords. It's thick rubbery underbody seal.
If it's the wing, the warranty should cover that.
For 'waxoyl' type stuff, I use VW's own cavity wax which is available from the dealers in spray cans. It sticks to stuff way better than the Finnegans junk!