Hi plasticAF, I have been told what I have been told, so its our choice to believe it or not really. With info that has been passed to me before from my mate, I'd definatly consider this the truth!
Where did you find the info on 737s and 757s in Belgrade?
I tried googling belgrade airport and I couldnt find anything to suggest what facilities it has, so I presume it must have a painting/engineering hangar?