OK, so I'm going to update this again, because it's absurd. Today I had to go to the office - 80 miles each way of almost entirely motorway. This is (realistically) the best possible use case for an engine. So I checked the service countdown before I left - 14,250 miles. Two lots of 80 miles...

Nope. 180 miles driven - the bulk of that was 2 x 75 mile motorway runs - and the distance to the next service has dropped by 1000 miles ! That would suggest <3000 miles between services. Crazy.

The service interval problem or the gunk ? All of them get gunked up. This is the first car I’ve encountered where it messes up the servicing schedule though.

I’ve just joined this forum specifically to reply to this thread ! I recently bought an SDV8 and although it was serviced (by a main dealer) 6k miles ago it was asking for another one already. Following this advice I checked the MAP sensor, very easy job, and this is what it looked like before...