carefully pry the black top off of the afm and clean the carbon track.
Don't use your fingers, but a q-tip and some 2-propanol, isopropanol or
rubbing alcohol.  OR better yet, get some laboratory grade ethanol or
methanol or isopropanol. Take the q-tip and gingerly scrub the track.  I'm
not sure i fyou can scrub the wiper though. I don't think i was able too.
Maybe you can slip a thin piece of cotton under it to clean it.  IF there
is a really bad burn spot in your afm track (you'd see it- mine was very
obvious) then you may have to bend the wiper arm to a new track. This is
very risky and can result in having to purchase a new afm. Yikes, $$$.  So
that is a last-ditch effort. You can also check the continuity of the afm
by putting an ohm meter across the leads on the afm connector and see if
it smoothly goes up (or down) as you move the flapper. If it has some
funky jumps then you may have some issues.  I'd probably do that before
you even bother taking it's top off.

be sure to seal the top on with RTV (silicon cauking. when there is a
hole, put cauk in it...) to keep water and gunk out.

cheers
M

Matthew Pollard          "Racing with the wind and flirting with death
Dept. Of Chemistry        So have a cup of coffee and catch your breath"
University of Idaho
www.uidaho.edu/~poll7356