I was searching for information on my Donnelly model number 240 and I found this thread, and it helped, but I thought I might add something.
The appropriate way to remove the button on this particular mirror is actually to twist and remove it rather than to try to push it straight back. The clip inside wraps around an "anchor" that is elliptical (oval shaped). The wider part is on the left-right axis, so when you twist the button 90 degrees, you align it with the narrow part of the oval so that the button slips right off.
Still, it is pretty hard to twist the button with just your hands. I stuck a screwdriver in the slot between the button and the mirror part for leverage and it twisted off pretty easily.
P.S. My car is a 1999 Subaru Forester L AWD.
Saturday, June 19th, 2010 AT 10:36 PM