repaired a loose, wobbly driver's side mirror by transplanting the adjustment motor, plastic gears, and glass from a complete 1985 325e mirror i got on ebay. the old motor seemed to work and the glass was ok, it was just the plastic motor housing that was cracked and allowing the mirror to wobble around.
the mirror glass from the 85 325e is thinner and seems less "zoomed in" for a wider viewing angle. not sure why it was more zoomed-in for the 88 m3. i really liked the multivex mirrors i had on my exige, so maybe i'll just end up getting those.