Both,
Valve seats because the gap (in the attached image) was greater than the tolerance ( range : 0.1mm < a < 0.5mm ) mines were > 0.7mm, one was 1.2mm
, I think that this clearance is very important in diesel engines, it affects directly the compression.
I've already used several diesel additives, and last sunday I checked my IP, result : all is OK , injectors were at 1015PSI (this was done to avoid noise : but the car leaks power) now there are set to 1450, the car runs better but is slightly noisy than before.