The one on my '98 ZJ did the same thing - it wouldn't pull in, but if I had it turned on I could open the hood and knock on the front of the clutch to help it go, and then it would work.
In taking apart the one from my parts jeep to do the same fix you're talking about, it turns out there's a little shim underneath the bolt that holds it all together. The one from my parts jeep had a thinner shim, and that difference was enough to make it work again - the only part I ended up swapping was that shim.
With that in mind it might be worth just pulling the front clutch plate off of the coil (on mine you can do that without removing the belt) and seeing if yours has the same thing. Basically what happens is the clutch gets worn to the point where the air gap exceeds the pull from the magnet. Might be able to just shave the shim down a little bit and see if that fixes it (it's screwed anyway).