Here's the issue, since apparently some people don't quite get how the problem happens.





The bolt bottoms out in the block, causing the torque to LOOK correct (since it has hit the bottom of the hole) without actually stretching the bolt. This causes warping between the head and block because the bolthead is not pulling that corner down against the block.

It may not always be the hole highlighted in the second pic. That corner bolt is the most common, but if you experience a headgasket leak around a different head bolt, check the depth and possibly trim both head bolts.

At any rate, not all 420a's are affected, mostly 96-98's. I have yet to see a 99 with the problem. Head studs (instead of fixed-length bolts) of any kind will fix the problem.

NOTE: This is all a RUMOR. If it were an actual engine machining defect, Mitsubishi would have recalled and fixed all the affected DSM's right?! (Think about the word "crankwalk" for a few seconds before you answer that.)