ArtBasement

Hi all, I've had my '02 ML55 for about 4 years and 30K miles. Suddenly the car has started a severe misfire; you can barely drive it. I've swapped ignition components and fuel injectors around, but misfire stays and is always on #5. My mechanic says its a burnt valve and wants to swap in another engine to the tune of $6K. He recorded 0 compression on #5, but when I try, I get 90 and just 10% leak down. I've tried seafoam into the intake and mixed in with the gas; no change. Sometimes I can drive with no sign of the misfire, but then it suddenly starts, usually after having idled, at a light for instance. P0305 is currently the only code. The #5 plugs are usually wet when I remove them. I saw this video and started thinking... could this be a thing?

Where do I look for the computer? Could a bum computer cause this? And I I go and remove the heads, are there any instructions for removing the heads anywhere?

Thanks for any thoughts or input -- Erwin