THERE ARE NO SEALS,as such, if std turbo, so one myth gone.
A certain amount of backressure is indeed beneficial to oil control past the turbo shaft, but you can have the turbo rebuilt with 360 and STEP GAP SEAL which will ALMOST totally control the oil loss, through the turbo.
Losing backpressure can allow it to develop more power, and a lot more noise!!
tabetha