Loose Outside Mirror Housing
 

I have a 99 Miata. The housing on the outside mirror on the passenger side
no longer snaps in place. It rotates freely. The control of the mirror
itself from the switch on the dash is OK. It seems to me there must be a
spring somewhere that's supposed to pull the mirror housing tight against
its base so that it stays in position. This spring (or whatever) appears to
have suddenly stopped working. How can I fix this?