The problem with vinyl tracks is the plastic they are made from. You don't know how old those tracks are. The add a material called a plasticizer to make them soft. As time goes on, the plasticizer will exude from the vinyl. This will make them stiff, shrink and is what causes a problem painting. If the tracks are too stiff, you could slightly warm using a hair dryer. While warm, roll them and shape them. Once cool they should hold their shape. Also while warm, if a dry fit tells you they are short you can carefully stretch them.
All in all they are a pain but they can be worked. If you can find an aftermarket track you are most likely better off. But on some models, (like the M107 SPG I just finished),you can't find an aftermerket matching track. In that case you just have to buck up and deal with it.
If you clean the tracks as previously stated in this fourm and try some things like I stated above, you can paint your tracks off the model and get them to fit
Good luck