Wow. Let's see. Where do I start. OK>>>
First of all, if there is bluish smoke coming from the tailpipe, that USUALLY indicates an oil problem. So that part is probably correct.
If Mercedes is blaming the previous owner for not changing the oil, I'm not surprised. I can't say if the rings are shot, but if they are,
and that is what is causing the problem, then there is only one solution. Well, actually two. You can take it to Mercedes and spend the money to fix it, or you can go back to whoever sold you the car and take it up with them. Of course, you know what's going to happen
if you do the latter. It will be like trying to get a dog off a meat truck to get them to pay for it, I guarantee you. Now, listen carefully to
this part>>>there is NOTHING that can "expand" piston rings and repair them if they are worn out. Nothing. Any magic elixir is only a
good way to flush good money down the toilet. If you choose to replace the rings on that car, 4K sounds cheap. It's an ENTIRE engine
disassembly and you know there are going to be other costs. JUST the supercharger alone (under warranty) on my C230K was 3.5K.
So, there you go. Sorry to drop a bomb on you, but whatever you do, don't start pouring junk into the engine. My own opinion would be
that you should go to a good independent garage and get another opinion (diagnosis) even if you have to pay a bit for it. OR>>>you could
call Mercedes Benz of America corporate and get customer service and tell them your dilemma and say that your car is still under the
factory warranty and the dealer refuses to take care of you, and that they are going to lose a Mercedes customer for life if they don't
take care of you.....and see what happens. Hey, it's worth a shot. Nothing to lose and a lot to gain if they can help you.
PS> It helps to cry a lot while you're explaining your dilemma.