Mercedes 560sel

Hello,

Blue smoke out of the tailpipe means that the oil is entering the combustion chamber and burning as the engine runs.
There are a number of reasons why engines will burn oil like this. It could be due to the engine having too much oil, leaking valve seam seal, broken piston ring, too much clearance between the block and piston.

Take a look at this guide, it covers the typical reasons for blue smoke:

https://www.2carpros.com/articles/blue-smoke-from-engines-exhaust

The best option would be to take a look at each possible cause and take appropriate action.
One way you can check if it is the piston rings, is by first testing the compression on each cylinder. If you have a low cylinder compression, you can pour a tablespoon of oil into the spark plug hole and test the compression again, if the compression rises then the issue is likely bad piston ring.

https://www.2carpros.com/articles/how-to-test-engine-compression

Please let me know if you have any questions.
Thank you.