have for about 20 years. Engine oil, trans fluid, gear lube, grease, air and oil filters... I have followed the recommendations set forth by Amsoil which are generally 1 change per year or 25K, whichever comes first. Probably my best story involving it's use is from the 1990 300E. At purchase it had 123K and used some oil (maybe 1Q in 2000 mi.). I switched to Amsoil and the oil consumption immediately started getting worse. 2000, 1800, 1500, 1100 miles... Then it stopped using oil. Now I change every 10K or so per their recommendations and it is using 1Q every 5K on average. I usually change when it's time to add the 2nd quart.
The thing that gets me the most is the fact that the average car owner is still stuck in the old 3000 mile change interval that has been around since the 60's. We now have 100,000 mile tuneups, 100,000 mile spark plugs, 80,000 mile tires, 500,000 mile engines and as a rule everything on cars lasts longer than back then. Why are we still married to the 3K oil change, especially when the mfr recommends intervals from 5K to 10K and up? I know, it doesn't hurt to be conservative but with everything else in the industry having been improved drastically over the last 40 years, doesn't it stand to reason that oil has been too? Dino oil is improved also, I might add.
Anyway, not a salesman or anything, just a satisfied, long-term user.

__________________
1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".