cleaning v-brake arms with riveted inner sleeve
I have had these brakes before, and what I've found to work is:


Take the brakes off the bike
Clean the bosses on the bike, inside and out with rubbing alcohol and a Q-tip (a.k.a. cotton swab)
Clean the portion marked in red with a q-tip dipped in rubbing alcohol. also clean the back surface of the brake (where the bolt is, but on the other side of the head in the same way). Be pretty thorough; you'll go through a bunch of q-tips until its clean. 
Let the rubbing alcohol dry
Grease your brake posts and bolt, and re-assemble. I use regular old white lithium grease.


They tend to last about 2 years this way (but I think we probably have a lot more road salt and gunk in the Midwest USA than Germany), and then no matter what I did, I had to chuck them (which isn't a huge loss, they're pretty cheap). 

The Single Digit 7's are more robust in this regard.