PLEASE CHANGE YOUR OIL!
I enjoy working on vehicles. I do not enjoy taking engines out and replacing rear main oil seals. GM engines have enough issues by design, add a few skipped oil services and then you have this. PCV system clogged up, excessive pressure in the crankcase built up and blew the rear main seal out. Oil leak? YES!! Major leak. Expensive? you bet! keep your oil changed and check it regularly.