With all the immunities and the acid damage to weapons, the only feasible way for a lvl 4 party appears to be magic missile/sound burst (or equivalent) spells.
Can anyone give me some insight on how to defeat a grey ooze?
Sorry, I'm on the pro ooze side and I'd like to see more of them win. Electricity will fry the thing. As will sonic attacks and, it seems acid ones. Just don't get into melee with the thing and your fine.
They're not actually immune to weapons, are they? You just have to be willing to have your weapons dissolved when they hit. A typical fighter ought to be carrying at least a couple of missile weapons and back-up weapons, and gray oozes don't have enough hit points to stand all that many hits.
Cast Protection from Elements (Acid) on your main fighter and let him go to town on it. He and the rest of the party (using ranged attacks) should be able to kill it before the spell runs out.
Would I be incorrect in assuming that the Ooze in question is one in a certain abandoned moathouse?
If so, my players are about to run into it, AFTER expending all their spells fighting *BLANK* and being pretty badly roughed up - I think pretty much their only hope is that it only has a 10' movement rate.
Hey, if all you care about is getting past the ooze, the 10' move should mean you don't have a problem. If a party is losing weapons, doesn't have a lot of hp, and no missile weapons, they had better consider running or die. I looks like an easy monster to beat if you just don't get near it.