Classic miror

Having recently folded the driver's side mirror on my Range Rover classic, I found that on returning it to the 'driving' position it appeared to be slightly loose. There is form of plug on the underside that might(?) give access to the mechanism, but it seems to be made of the same material as the housing itself & I'm not sure if it's meant to be removed. I do have a complete spare unit but would rather save it, in case of future damage & repair the existing mirror if possible. I've not had this problem before on previous RRC's despite folding the mirrors on a regular basis - any ideas folks?