Conservatively, over the past 8 years, my husband and I have done maintenance, repairs, and upfitting work on our Interstate that probably would have cost us $30,000 in labor alone if we had instead hired it out.
Every Interstate owner should consider becoming a DIYer, or if that is not a personal preference, then find an independent mechanic if the vehicle is out of warranty. They will be cheaper than MB.
And of course use the forums to help troubleshoot. This sounds like it is probably a Sprinter issue, so Sprinter Forum
may bear more fruit than Air Forums.
Do your research first, though, because Sprinter Forum is more of a tech-oriented rather than a social forum, and therefore it is home to a lot of users who become prickly when faced with questions that they consider to be lazy or un-researched.