Tuner mods
RENNtech upgrades are definitely available for your car, and in my experience most dealers know of RENNtech and respect their quality. The ones I've dealt with don't have any warranty issues with them. I am a new RENNtech distributor, so I am a bit biased. I know some dealers don't want anything to do with any aftermarket parts, but it is against the law to just say the warranty will be voided if you use them. Also, there are plenty out there who will work with you.
Hartmut Feyhl, the founder and owner of RENNtech is ex-AMG and has a really good relationship with M-B; there just are not issues with warranty or quality.
If I can be of assistance in providing info, pricing or even parts, post to this forum and I will contact you.