Thanks v much for this useful thread!
I believe my slk is leaking as well and I sure hope it is the same issue as is identified here with this simple fix.
I noticed in another thread a user suggested to put some oil around the seal before inserting the replacement gasket... and in this thread it was mentioned the following:
The plug opening should free of grease or oil. No sealer should be used in the installation of the new plugs
Should I use some oil to help it seal better or just plug it in? Thoughts? Suggestions?
The MB tech said not to grease them along with the service bulletin. So I would opt with "no".
I replaced mine without using a sealer/lubricant before I drove 2200 miles to California and I have no leaks.