The caps should be changed fairly often, they are servicable item. Crankcase pressure is purely down to worn bores/rings - ie large clerances. A new engine barely breathes at all, but as mileage increases, combustion pressure will begin to get through.

It's not really a problem, providing the breather system is upto it. Sadly, CVH breathers are not upto it when new! First port of call is to check all pipers are clean. If you still get the cap blowing off (not uncommon under boost) then plumbing the breather system to breath to atmo (or catch tank is she's really bad) is the best option.

Oil being fed back into the metering head is the reason you get oily boost pipes - not because the turbo is worn! This oil is not good for the combustion process, effecting the speed and shape of the flame front, and promotes detonation.