I have a '96 C220 48K miles

The single wiper has always worked fine.  Recently, it seems to hiccup
in the middle of the motion pattern.  For half the motion (in the
middle), the wiper goes slow, or very slow.  It is almost as if there
is SYRUP on the middle portion of the glass that holds the wiper
through that part of the motion.

The problem stopped for a while, and started again this morning.  I
thought it was the blade since the problem has seemed intermittent.

This morning it was raining pretty hard, and the wiper is driving me
NUTS!  It clears slowly, but I also am tentative to use it, since I
worry that might burn out the motor.

PLEASE HELP!