These 'ears' are a big nuisance (Thats me holding back my true thoughts!) All parts are replaceable now. I had to replace the insert( white lens indicater lamp cover) within the ear. At the time parts were not available. That said I never had to take it apart to fit it. All I can offer you is, when pulling the mirror to inwards position (as when parking up in a street) it seems that it has to ride over some form of raised area? certainly it offers resistance and the extra push is needed to lock it...has this worn out do you think. I know that on mine it was always/is always an extra push for the 'stop' position. I dont know more than that I am sorry, as like I say I did not have to remove anything to just fit the lense, that was taken out by a speeding Ambulance. It was either that, or hit a high stone wall in Somerset! The lense as a part was £30.00....New wing..who could guess? Try a breakers yard if you get stuck and it is shot beyond repair.
I had to change the mirror after getting it broken by a white van. Bought a short arm one on Ebay for £40. After changing all the glass and wiring and fitting the mirror it would not stop at the right position. Solved this by putting a flat washer between the ridges, setting the position and tightening the bolts - problem solved. Hope this helps.