Mass air sensor: repairable?

["Brandon Hull" <brandon@cardinalventures.com>]

Well the Ersatz S2 is up an running, but badly:  rough and stumbling above
idle.  Error codes indicated mass air sensor, and sure enough when George
swapped in the one from his car, things clear up.  The problem appears to be
intermittent; at least once they were able to clear the codes and rev the
engine.

Anyone have any experience with rebuilding or refreshing the MAS?  Any easy
fixes or common failures?  I didn't notice the problem when I heard the
engine run in the donor car many moons ago; anything about sitting or
storage that would mess it up?

Thanks.  I really don't want to know what a new one costs...

Brandon
'91 Ersatz S2 (Coupe Quattro + '91 3B 20vt)