Not sure if the flag mirrors on an SC are the same as my 87. Both of my original mirrors have fallen off and it is a known problem. The first one fell off during my test drive!
The mirror glass appears to be attached with a rubber looking layer on the plastic of the mirror unit. Over time it detaches from the glass and it just falls off. I have heard of people just getting a piece of mirror cut at a glass shop and gluing it on the backing plate. Mine fell off 15+ years ago so a whole replacement mirror was pretty cheap but the cost may have risen to the point where a cut mirror is an easy cheap fix.