[saxonb]

Only noticed this recently due to a potential buyer pointing it out. His mechanic advises that the engine needs rebuilding (!) but can't provide any detail on what specifically the issue would be.

The engine runs perfect. Has had genuine OEM oil every 5000KM. Any ideas what this residue is? It it is a bit loose and can be wiped off with a finger and turns into tiny black seemingly carbon particles.

My initial research is that it's caused by not enough driving and deposits of moisture and acid which would otherwise be vented through PCV if I were to drive normally at full temperature for long enough. This makes sense as I haven't been able to drive it much for a far amount of time.