Pardon me if someone else has already posted this, but I think I came across it by myself. A company in California has a short YouTube video on how to check if your B-Class motor has leaking coolant seals:
There is also a mention somewhere of their selling new seals for this. Unfortunately they're in California so I'm not sure if it's worth shipping your car to them for repairs. I'm on the East coast and I'll bet it's $2000 shipping each way.
I did have the Mercedes dealer check this for me at my 4yr/40K maintenance. They did the test for free (everything else was $790). Bad news is that my 2014 has a good old leak underway. I have two months extended warranty left, so the tech told me to drive like hell for the next two months. The dealer can't do anything until there are actual problems or error codes, and when they do do something its has to be a total motor replacement. They don't open up Tesla components and do internal repairs.
I've emailed QC Charge for advice, but no response yet. Perhaps this is a job for Rich Rebuilds...