Speaking of lens disassembling, I have taken apart my 16-45 lens. I don't know what happened to it, but one day all the middle element started to rattle inside the barrel. It was realy hard to open it, but about 100 times harder to put everything back. Before that I've opened one cheap AD2 zoom and one offbrand lens, but these plastic modern lenses are next level.
Actualy I was surprised, how cheaply it was made, realy, not for DIY enthusiasts
Of course I did not fix it, because I couldn't find the problem, so it still rattles and makes blury pics.