pursy:
I worked in the workshop for Taylors of Martley,they ran some 8lxbs and 8lxcts day and night. The night trunk was Worcester to Carlisle and the day run would be perhaps down to Devon. They would like a gallon of oil each shift.When you finally got the engine to bits the bores,rings and pistons were about knacked. If you just tried to put just rings on them the piston would drop down the bore without tapping it.
If it got really cold the only way to start them was to remove the air filter element and get a fire going.
Valve guide wear was bad too, leave them and the valve would drop and really spoil the fun.
But having said all that I loved driving them especially the 300hp 8lxct the torque was pretty flat from 1000 to 1500 rpm and that was when everthing else wouldnt pull below 1400 rpm.
Funny thing was when you poured oil in them and they were worn out they still went the same and were excellent on fuel
Sounds like you could have been using Engine oil of too higher spec (Turbo engine oil!) IIRC you only needed to use a basic lube oil,I’m a bit hazy on this point but IIRC Gardners didn’t recommend the use of the high quality oil.Maybe some of the Gardner experts could confirm or otherwise ! Cheers Bewick.