The old Warhammer Fantasy plastic models are actually terrible and significantly worse in quality compared to AoS plastic (Except for the kits still available on the webstore). One of the main reasons why I am selling away +10 000pts worth of High Elves (With over a third of the models still unassembled, including 2 HE battalions) is because I don't want to spend a month just preparing the parts for assembly by carefully removing the horrible mould lines and fixing all the errors with greenstuff in disfigured plastic parts. Not to mention the old plastic is much more fragile and breaks easily. Also, I'm pretty sure it ain't just bad luck with the plastic, since I had similiar problems with my Bretonnian Army (1000pts) and there is a difference of 5 or 6 years between buying these two armies from different sources.
Looking forward to what Warhammer: The Old World has in store for us.