Personally i never had the problem but i think what’s happening is as the engine warms up, oil warms and thins out, o ring is prob cracked and as it gets warmer the thinner oil is getting by the cracked oring. I would, as you stated, dump a cleaner in the motor, change the oil and look for metal, change oil filter and get a new good oil filter but cut open old filter to look for metal, and do the screen and sensor. Honestly, youre in a situation where you dont own it and dropping the pan isn’t really feasible, UNLESS, you really want the truck. Personally, i would do the o ring before I bought it and if it doesn’t work buy it and drop a jy motor in , fix body and sell it.