I am going to throw one at you. I have twin Ford Daganheim Lehman Diesel
6 cyl engines in my GB. It has over 3000 hours and I was using Delo 40W straight weight just like all the diesel guys here did. When I started it smoked big and lots of sheen on the water. I could go about 50 hrs before it really started using oil
and I would add at least a gallon or more per engine before the 100 Hr oil change
Then I decided to go synthetic because everything I own since 1977 I use Mobil 1 synthetic. Everybody said "you can't put synthetic in an old engine" and I said why not?
Bought Delvac1 and changed one engine. Started it and immediately I could see less smoke. Then the water out of the exhaust check, I always do, and I notice less sheen. Took the boat to the Island with only the one changed and I could tell a big difference. Changed the second to Delvac 1 and since that change at least ten other GB owners have done the same. We all experience less smoke and sheen and much less oil consumption
That was 1998 and I have a 10 yr history
with Delvac 1
It is because the sheen is unburned diesel and the synthetic has a much higher lubricity factor and seals
the pistons better. You try it.