Was wondering if anyone here experienced something like this. I bought a 2017 w205 c43, which had 6 months factory warranty on it. Purchased an extended warranty for 100,000 miles.
Contacted Mercedes of Englewood NJ via phone to ask if a resonator delete would void warranty, was told that it would void warranty on the exhaust exclusively considering it's after the cats.
Completely OK with this considering the exhaust after the cats consists of steel and quite inexpensive to repair and unlikely to require a warranty to repair it.

I smelled a burning smell last week and decided to bring it to mercedes for them to check out the source of the smell, as well as an issue with the "roughness" of 5th to 4th gear in sport plus manual mode.
They are telling me now via phone call there is an oil leak from the gasket for the dip stick which is causing the smell as well as the "driveability" issue with the shifting, and due to the resonator delete they can't
honor the warranty at all.

First of all I know for a fact the resonator has nothing to do with the gasket on the dip stick on any car. Second The dipstick has nothing to do with a gear shift in a specific mode on any car. Third of all I feel repulsed
that I legit asked for permission before removing the resonator and they are now denying that anyone has said, or would say that.

Any advice?

Unfortunately, a warranty is only as good as the honoring party. No good answer to your problem without threat of legal action (preferably from an attorney). Expensive exercise, as one pays their own legal expenses.

I mean this isn't an issue, I'm going to threaten with my attorney I have one on retainer. But this issue have you heard of it before, assuming it's even real?

Did you get that in writings? Your lawyer has lots of ***** if he is going through with any lawsuit without any proof, just what he said she said.

dont necessarily need it in writing for this case. Rather to provide an expert in the field that can state the issue in question has nothing to do with the resonator. Similar to if your transmission goes and Mercedes wants to blame it on the brand of wiper fluid you’re using

Reinstall the resonators and prove issue is still there? Not sure why you would pay for an extended warranty and then “modify” the car. Like any form of “insurance” the party responsible will exhaust every option not to pay out. You should have banked the money in case something major comes along. Sorry for you luck but I don’t like your chances.

***update***

Spoke with dealership, gave them a hard time with no resolve. Spoke to an old colleague 15 year engineer for MBUSA, who left on good terms when they relocated to Georgia. You can dispute cause of issue with MBUSA and they assign an engineer to your case to see if it should indeed void warranty entirely. I did not have to deal with this, my colleague called the GM for the dealership and assigned the foreman for the shop to my car. Everything is being fixed, warranty honored. The resonator does not in fact effect a gasket in the engine bay (duh).