Rear main vs tranny input seal leak

[RICK LAKE]

Texas Doc Happy easter to start with.
Looks like a problem with the real seal being installed. Either too much RTV or the seal lip was damaged from being off side in the rear cap. You will get this right after a couple of trys. Everybody goes through this.
2 times, IMO throw that Mr gasket breather in the garbage or hang it on the wall. This is why the motor is building up pressure after a couple of minutes at cruising. You motor vacuum is between 10-14 hg vacuum and the small hose with the breather can't supply enough to keep the inside of the motor under vacuum. Pressure builds up and you start leaking. Look for a K&N valve cover filter that looks like a small air filter. If you need a picture, look at dirt track motors. That breather was designed for sitting on the oil fill tube on some old motors like AMC V8 and others with filltubes that stick up about 6" They where hook to the air cleaner but worked both ways of letting fresh air into the motor and letting oil vapor out and being burnt up by going through the carb. Repair this, your oil leaks will be fixed. Happy Easter Rick L.