I had a leak at the rear cam plug (note that this is on an '89 3.0), which I found by using one of those dentist's mirrors. Very handy little gizmo's. To replace the plug you have to slightly loosen the bolts holding the cam bearing caps (do it in the order suggested by the manual) and the plug will slip right out. Reverse is just tightening the cap bolts in order to the correct torque. Not hard once you get the valve cover off.

89 Montero 3L. Stock.
Rust and Repairs at Equilibrium