I replaced the valve seals on my 91 at 120,000 miles and it didn't fix the problem. Once I replaced the heads, the problem was solved. The seals were definitely bad but they weren't the only problem on my engine.

I'm not sure if there is a way to tell when the valve seals are enough or when the entire top end needs to be redone. Anybody have any ideas?

1991 Montero LS, fading red paint
Front and rear limited slip differentials
95 SR Rear Springs, torsion bar crank, 137,650 miles
33x12.5 ProComp Mud Terrains, Bushwacker Fender flares
3 litre V6 with new heads