560 oil consumption
 

Here is a mysterious one:
1991 560 SEL with 62k miles in excellent condition, service history, etc. is burning about 1+ quart of oil per 400 miles. Topped off 1/12 quarts last week and reset the tripometer....425 miles later the oil light came on.
Car runs fantastically, gobs of power, no smoke whatsoever.
No leakage whatsoever, no oil in coolant system.
I am aware of valve stem seals being problematic at much higher mileage, but??
Any direction here is much appreciated, though I am thinking compression and leakdown tests are in order here.

was your car parked for a few years? Mine was before I got it and it did the same thing as yours. Thinking I needed a major engine job I thought it would not hurt to try some Wynn's additive for sticky rings and valves. 1000 highway miles later - my oil burning went to nothing. 4 years later it still does not burn oil. I will only suggest you try it if your car was sitting for a long time which could have caused the rings to stick. Judging from your low mileage - it could have been sitting a lot.

If it was a Jaguar XK engine, that would be considered quite good consumption!

High Oil Consumption
 

You need new valve stem seals. My 981 560 SEL did the same thing (burn about a quart/100 mi.) with only 55k on the car and was told by a local Benz shop that the seals are too soft and all of them came that way from the factory. They do em all the time at this shop. Mine luckily was under waranty, $2500 job. Both heads came off and valve job with new harder seals and has not leaked or burned a drop since then which was 60k mi ago.

Check the oil that's in the car; had mysterious oil consumption on my 560SL (148K) after the first oil change under my ownership. Found the shop had used 10W30 in a Michigan summer; took it out myself and put in 20-50 as per manual, in a high-mileage-engine formula. Now I'm making 3000 miles to the next change without dropping to the point of adding oil.