I've seen on youtube these guys saying that they fixed the folding mirror problem with some WD-40. It made me curious so I tried it with some greaseless lubricant. It did not do the trick. Myth busted.
I noticed after purchasing my CX five GTR that the folding and unfolding was not exactly smooth. I sprayed WD-40 in the gaps between the mirror housing and the arm that holds the mirror housing. Just make sure to clean off any overspray and make sure to open and close mirrors repeatedly while spraying the WD-40. After doing the above, I found it smooth out the opening and closing of the mirrors And may cure the problem you are experiencing.