at this point...I myself would break the whole motor down.
the person you bought it from obviously raked you over the coals, and sold you a bike/motor that's clapped out....better to tear it all down now, and replace all the bearings and all the seals....then you KNOW what you have, and aren't "hoping" the guy that sold you it did it.
otherwise you could be having constant issues...and breaking down out in the woods, or where ever.
it sucks, I know...I've been there....that's why any used bike I buy now, gets COMPLETELY torn down, and completely gone over, with all new bearings and seals....and I don't mean just the motor...everything.
you can get the bearings made from a local bearing shop if need be...that can save you a lot of money.
OR...you can sell the motor, and use the money towards a newer motor.