Interesting the comments earlier about based fuel at supermarkets being a lower grade. First time I have heard a proper explanation for why its poorer.
I did some stuff on this at Uni years ago. Not to the level the other Chap on her obviously.
You could see the residue forming which was then cleaned by the additives that had a higher boiling point than the fuel.
When I say cleaned I mean carried forward into combustion rather than building up on inlet & injection system.
I would be intrested to know what length of time it would take using cheaper supermarket fuels to impact an engine adversely. 5k, 10k, 50k.
Because there are a lot of people using it.