A 3P company really needs to make an upgrade kit for the knees (or if they have, someone please provide a link!).
Yeah one of the knees on mine stopped working. It was fine, but then after the third transformation it wasn't (it's not because I was bending it in a wrong way or anything).
Tried doing the glue fix as you've linked but it didn't work for me unfortunately. For the time being I've just left it and accepted one knee will move differently to the other.
It's been a while since I looked at whats going on inside the knees, but from what I remember there are three separate parts that are all supposed to work together - only two of which have gear teeth.
Over time instead of using the gear teeth to move, two of the three parts start warping and rubbing past each other instead which is why you get that smooth action rather than a ratcheted one.
A really poor design IMO. They either should have used 2 pieces instead of 3, or made the parts die cast (why not both even considering what this fella costs).
Looking to buy lucky draw Armada Prime and Diaclone Marlboor Wheeljack.