I have numerous B+W filters and I have been perfectly happy with every single one of them, until now.
I bought the 82mm slim circular polarizer MRC, which is a very expensive filter, and it is impossible to keep it clean. Having been a more than average active amateur photographer for +35 years, I have cleaned a filter or two in my time, but this B+W is just hopeless.
When I use pure ethanol and a special lens cloth, I am able to get it spot free (various other cleaning stuff has been used, but it does not work). As most of you will know, it is quite difficult not to get small finger prints on the glass now and then, when adjusting the front filter element. But a heavy breath and lens paper usually fixes the problem. But the only way I can get this filter clean again is with alcohol and the special lens cloth.
If anyone have similar or preferably different experience with this filter, please comment. I wonder if there is something wrong with the coating on the one I have.