There are plenty of threads here on how to refurbish those ports. Those sketchy sliding ports are exactly the same as the fixed ports except the glass is in two pieces, with one piece hacked into the inner track with a few bits of rubber and a cross member glued in. And a drain slot cut into it. It is easy to see how it goes when you take it apart. Personally, I just replaced the glass with a single piece. Next time, I'll do as Jerry VB suggests and replace it with a standard opening screened port.