The p5 plus is a 5 port engine , only difference is the rear bearing has a larger diameter 25.4mm to 25.8 mm and the idle screw is now on the opposite side so it is easy to get to and yes the crank is .5 mm larger. as far as leaking bearings ? Yes NovaRossi did have a problem , due to a bad seal material ,it would shrink from heat , now all the new seals are blue , if you have a black one REPLACE IT !
RB Concepts even had bad bearing seals . So pay close attention to your seals on the front bearings.
The new Plus version is supposed to be a lot smoother from bottom to mid range , the regular P5 was an animal !!! If you want super smooth power use the 421 B , It screams incredible RPM yet is silky smooth EVERYWERE ! From idle clean to the moon ! I have never driven a smoother more powerful engine ! I have a modded RS 7 Crono engine and it is utterly insaine powerful but the 421 will eat it alive on the track because it is so easy to drive !