i had mine done under warranty on my last car ('07) when it had 74k. they replaced both wastegates under warranty with no issues or hassles. the car had 125k on it when i traded it in and the problem never came back.
my '08 is not showing this issue...finger's crossed. i just picked up the '08 yesterday so i'm going to take it to Maranello ASAP for an inspection before the warranty expires.
"Dead Serious" - '08 monaco blue E90 335i 6MT. sport pkg. premium pkg. black leatherette. brushed aluminum trim. M-Tech shift knob/boot. M3 mats. matte black kidneys. carbon performance trunk spoiler. blacklines. JB4. aFe stage 2 intake. resonator delete. mechunik plate mount. 19x9/19x10 +24 style 95's with 225/35/19 and 265/30/19.