whitish smoke from exhaust/carbon buildup

[Luca]

So I went for a dyno today and the tuner told me my turbos are on their way out due to this white smoke coming from the exhaust on deceleration.

Could it be anything else? I noticed oil on a spark plug after changing them, could it be the valve cover gasket? 02 sensor code before the cats is shooting a code as well although it's been cleared and hasn't come back since the plug/coil swap. Car runs perfectly, no power loss and is not throwing any other codes.

Anyone else having this problem?

09 135i
charge pipe/bov
vrsf intercooler
evolution raceworks catless dps
berk mids/street exhaust
dual cone intake
flash tune
bms occ