Pella leaky window?

I am in the process of looking at a foreclosure that is about 12-13 years old and had Pella windows installed. I have read about some of the problems of the older windows and concerned about that. I walked through the house and all the windows that are movable had the pain peeled away where the upper and lower window meet (so along where the latch is). It is across the entire strip and has some black spots.



I took my keys and pushed on it a little and didn't notice any rot. Some of the windows were not latched so I am wondering if this is from someone leaving the windows unlatched and just some moisture from the winter etc or a bigger problem. I will try to get some pictures tomorrow.



Anything else I shoud look for on the windows when I go back?





Thank you