All the Mitsu V6 engines have a crankshaft pulley bolt issue - it needs to be replaced with an updated bolt and tightened to the updated torque value or it can come loose and damage the crankshaft.

All the engines tend to have issues with the valve stem seals leaking resulting in bluish smoke out the exhaust, especially prevalent on take-off after idling for a while. Lifter tick due to clogged or failed hydraulic valve lash adjusters is also common on all the engines.

The 3.5 DOHC has an issue with the throttle butterfly valves in the variable intake manifold - the bushings in the shaft wear out causing a vacuum leak and vibrations in the shaft itself. If left unrepaired for long enough the butterfly plates can come loose or break and be ingested by the engine, causing all sorts of damage.

The 3.0 SOHC 12 valve V6 was available on both the Gen 1 & Gen 2 models, but the Gen 2 also had a 3.0 DOHC 24 valve engine available.

Limited slips were available in various models on both Gen 1 & Gen 2 Monteros, but the air locking diff was only found in the higher trim level Gen 2's. The Gen 2 locking rear axle is a pretty simple swap into a Gen 1, providing a beefier rear axle and rear disc brakes - the stronger rear trailing arms are often swapped at the same time and it's more or less a bolt-on upgrade (some wiring is necessary for the air pump).