ok, look at the side of your engine block, basically under where the spark plugs go. there's undoubtedly a bunch of crap there on the block. every jeep 4.0L i've seen has it. i'm thinking maybe there's a TINY head gasket leak that's letting out coolant onto the hot engine block causing it to burn off rapidly and never drip to the ground.
there is a member of capitaljeeps with a 96XJ with well over 150k, his doesn't smell.
none of us in the group have found anything suspect, but i know i lose about a cup of coolant every couple thousand miles, which has gotta be enough to cause the smell.
could be a clamp. chrysler uses these ubergay clamps to hold on the radiator hoses, well, all of the coolant hoses for that matter. they're spring steel. take those off a couple of times, then put them back on, who knows if they'll clamp as tightly as they did when new. i don't trust them. i replaced all of mine with stainless conventional style hose clamps, the ones with the little screw that actually binds down on the hose. that didn't help, it still smells.
i replaced my radiator cap with a levervent cap. that didn't do anything either.
could it be the water outlet/water neck/thermostat housing leaking onto the water pump? unlikely, because you'd probably see some crap all over the hood getting flung up onto it from the belt turning, but might be something to check out.