Maybe all know this, but no harm in repeating.

The easiest way of checking for leaky valve stem seals on a petrol engine.

Find a downhill,
let the engine run against compression (if auto-tranny, force the lowest practical gear)
floor the loud pedal and watch for white/grey smoke.
If smoke, most probably valve stem seals.

(The running against compression creates a vacuum in the cylinders, which sucks air and oil past the valve stems. This oil is burned when throttle is opened)

If it smokes under hard accelleration, it's more probably rings/bores.

1989 Exceed LWB
4m41 (3.2DiD TurboDiesel
5-spd Manual Tranny
2" lift
31" BFG A/T