Thank you for describing your experience. In fact, my "indy" mech had the same suggestion. But I decided to try once more, as I had come across a shop in North Seattle (European Motors Corp., 16017 Aurora Ave N) that works on Mercedes exclusively (they also sell used Mercedes, which they service & fix-up before selling). Anyway, when I presented the mirror to the young fellow there, he told me they see a lot of them... then proceeded to open it up by removing the housing from the frame and exposing the interiors. The spring had popped out. After attaching the mirror frame back on my car using the 3 attaching screws, he repositioned the spring using what appeared as a locally designed shop tool in the shape of a long shanked hook, and the mirror now works great (minus the self-dimming feature). Took him less than 15 minutes...
FYI, the housing slides back over the frame and snaps into position...

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Toni (near Seattle)
'98 E300TD 114K Miles
'77 240D Stick 386K Miles