I have owned many of those models over the years, and have never had that problem. The only way I can see that being a problem is if you move them around a lot, or worse, play with them like they were Hot Wheels cars. All the Schabaks I've ever owned sat on shelves or were left in their boxes. Not once did a wheel fall off.
I've ditched most of my Shcabaks, because they are too small, and the decals are damaged more often then they are correct.
I have a few left, if you are interested in them. I'll make you a good offer if you decide to buy all of them.
USAir MD-90 (not an MD-80. They took an MD-90 and put USAir decals on it. I have two of them.)
Muse Air MD-80
ONA DC-8 (USA Bicentennial 200 years)
Also, I know I have....somewhere put away... a Piedmont/USAir box set consisting of a USAir 727 and 737-300 in the rust colors, and a Piedmont 727 and 737-300.