slk55er

Had a puddle of washer fluid and although still under warranty, I decided to try a do-it-yourself repair 'cause the nearest dealer is 120 miles away. I removed the left front wheel and forward inner fender liner and found a pinhole-sized leak in a seam of the black plastic bottle. I emptied the tank with the washer pump and used a product called "RapidFix" which is a "welding powder and liquid activator" from my local ACE Hardware, but any plastic-specific epoxy would work. I also loosened the bolt which attaches the tank to the spoiler, thinking that some movement should be allowed to reduce stress on the tank. See the attached photo.

Re-installing the fender liner is awkward, but can be done. So far so good -- no leaks.

bop11

Good luck with the repair. Polyethylene is very hard to repair because of its 'inert to most all chemicals' property. Most glues and epoxy won't bond to it chemically. There are some that use a primer to etch the material such as those produced by RELTEK, http://www.reltekllc.com/product-pro...son-charts.htm, but I have never had long term good results with most when trying to bond to polyethylene.
If you just had a small pin hole in the "Knit Line" ( the line generated when two flow paths in the injection mold meet), the material you used will probably plug it, but if the plastic flow front was too cold when they met, the whole line is weak and suspect. Seems MB's tank provider had a bad process setup and many of these tanks got into the field. Since it is not a safety related item MB will not recall.
I once worked at a company that provided blower wheels for Chrysler and others. Since defrosters are safety related and the wheel subject to recall, we were very careful about the mold and melt temperatures and the injection rate to insure that knit lines were as strong as the rest of the part.
You might want to think about ordering a new tank, now that you know how to replace it. The complaints about this part seem to have diminished, so I think MB may have disciplined its source.

jamartsandcraft

I had the same problem. With the Covid-19 downtime I finally took the time to investigate. Found the same seam leaking. I followed another member's advice and used Gorilla plastic pipe cement that I found in the area of plastic plumbing pipe fittings. It's made for multiple plastic types. I applied 4 coats on the seam, allowing about 15 minutes in-between coats. I then waited an hour and filled up the tank. No leaks! Came out this morning and no puddle under the car. Also, the error message is gone! An advantage to using this cement is it came in a can with a brush applicator. Easy to apply on the seam.