This is my first post here but I used to be on the forum many years ago...just couldn't remember my user name, email password, etc...anyways.... I just bought a used 2011 yz450f, only test drove it up and down the street at the guys house and didn't notice anything irregular. When I got it home I ran the crankcase breather tube to a catch can located along the back of the main frame on the left side near the rear shock. Took it to the track and after riding hard for about 15 minutes or so it was spewing oil everywhere. Took it home and the output shaft seal had popped out. I figured out that the breather tube was kinked underneath the tank not allowing it to vent. I rerouted it and anchored the tube so it wouldn't get kinked anymore. Cleaned up the output shaft seal put it back in and started it. I pulled off the oil filler cap to top off the oil as it was running and noticed a lot of pressure blowing out the filler which seemed unusual to me, but I don't know these engines too well. Before I could top it off it was spewing oil again from the output shaft seal. Decided to do a leakdown test to see if there's a head gasket or rings problem. It was leaking a lot from intake and exhaust valves (only held 15%!) but didn't notice crankcase leakage. So down to the questions.... Should there be a lot of pressure in the crankcase when it is running? Wondering if the seal just popped out the second time because it was reused. Horrible leakdown test - Was it just so bad because the engine was cold? It seemed to pull hard when I rode it. Kind of lost here with this bike....I thought I bought a good condition bike.