blaster pulling oil into crankcase

[mookman]

hi, i hope someone can help. i have friends 200 blaster it came to me seized up
got a piston and rebore , all ok .a mile later bike stopped , friend forgot to tell me he had filled up the transmission side to the top with two stroke oil!!
ok, drained oil, filled to correct level, bike ran then sucked all the trans oil in to crank. i changed te oil seal refilled , oil went into crank.. stripped got a new collar as old one scored , new seal , correct oil level, oil goes into crank..
checked breather , blocked ok this is it , oil goes into crank...
now i can see the funny side of most things but this is getting boring.. i am thinking of running motor with oil filler plug out to see if this reduces pressure
why am i getting suction on the crank...
please help .... any advice would be great
thanks in advance ,
mookman