I think I found the problem. My Jeep is a '95, and the replacement part I ordered is for a '95, but the part they put on the '91-93's actually screws on from underneath. I'm thinking this has got to have one of those on there, or else it would have popped out. And I'm pretty sure this is true, because the original part is black, but the replacement I got is gray, and the website shows the 91-93 part in black. So the valve cover is going to have to come off in order to replace it. Gotta love it!