if the oil feed is standard it should be fine,oil presure have you put an uprated pump in there?

the seal can still leak even if its new ,engine may be poor condition
the seal does not seal completely as you ave to have movement in the shaft
it relise on exhaust back presure, bigger exhaust bigger turbine housing
lessens back presure and can cause a problem

20/50 oil makes the turbo larst longer ,most turbos are running higher than standard a get a lot hotter
better protection