I am somewhat obsesso about laying bulletproof track, and have used a lot of re-lay flex (some, Shinohara, has been used in several different places on a number of layouts since I purchased it in 1965.) Even when using brand-new, fresh out of the box material I give it a thorough inspection, and immediately correct any irregularities before they can become problems.
As the OP said, two minutes worth of checking and correcting can save two hours of corrective action later. It might also save that favorite piece of rolling stock from a plunge into oblivion.
Chuck (Modeling Central Japan in September, 1964)
For years, I have been reading about reusing track if you gently slide a putty knife under the track. Today, when running a train, the locomotive derailed. I watched it run back and forth over the offending spot. I noticed the locomotive and cars rocking slightly. Upon closer inspection, the inside rail had vertical kink in it. It wasn't where a rail joiner was, so I looked even closer. I must have bent the track when removing it. 2 hours later, I had the offending segment of track cut out and replaced, soldered in place and ballasted.
IF you're going to reuse track check it thoroughly before you do. 2 minutes of closer checking would have save me 2 hours of replacing it. When the diluted glue dries, I'll paint and clean the track. Lesson learned.
Marlon
See pictures of the Clinton-Golden Valley RR