According to him, no has never over filled it, says he goes by the full mark on the dipstick, as far as age im unsure however it looks fairly new and he says he had bought the engine a few years ago new / replaced old one with new of same type had repair shop order motor n install it. Ive heard something about a reed valve that could need to be cleaned that works in conjunction with the crankcase pressure and if gets stuck this could possibly happen, however unsure of location of such valve. Ive also heard the same as you asked amongst a few other things. Just trying to get as many possible solutions as i can.
