this problem with the wiper just won't go away. I took the car to the local MBZ dealer and they lube the linkage again. Still the same problem!
I tried banging on all the relays behind the fuse box and that didn't seem to make the wiper better or worse.
It does seem to be heat related. If I haven't used the wiper all day it works fine for the first 30sec or so, but after that it starts to slow down and jam.