High miler 940, running like a dream so far, thanks.
 

After excellent advice and support on here, Facebook groups and YouTube videos, I can say my leaky, asthmatic old recent blind ebay purchase has dispelled my concerns by doing 800 miles in th last few days, laden with emergency tools and fluids, guitars, amps, speaker cabs on th outbound journey, many people during th intetmidiate period and th tools and seven excited rescue greyhounds on th way back, still a slight oil leak to address soon, but, after getting her back to base settings, she cruised faultlessly, pulled well and averaged 34mpg, which I'm staggered at, but I've done th sums twice now!
So thank you folks, that's part one of th plan complete.

This must be 34 miles per imperial gallon?

Aye, I'm basing my surprise on th figures of my last old tub, another 940 with a B200, that barely made 30mpg on a run, tho it was an auto with overdrive, but at 90,000 was probably not quite run in....