Rear window slider not working correctly.

[Dralphie]

I’ve recently noticed that the back slider window is extremely slow to open, and often will stop about halfway. It closes normally without issue. Anyone run into this issue / have any idea what might be causing it? I checked the track and I don’t see anything that would be causing the problem. The window was left cracked about an inch one time that it rained, but the inside was almost entirely dry and I don’t imagine much rain would have gotten in. Plus it worked fine for a long time after that happened and just recently started having the issue.