£180 is ok labour rate for changeign the rings but your bill will be much bigger.
i have done quite a few nasty, intresting and fun things to vw motors.
i have never yet managed to kill the rings. you can puff enough air at them to make over 400 bhp with std rings, i'll put money no you have damaged pistons, esp as you have said it runs a bit lean, detonation car crack the top ring but it can also and normaly dose eat at the edge of the piston and expose the top ring, on engines useing spacer plates or offset bushes this is an even bigger problem as there more det prone.