Soundproof sliding window

I have some windows in my 12 year old home that we have been unable to determine the name of the manufacturer. I have had at least two contractors look at them and the best I got was the name of a stock supply company that dealt with my builder 12 years ago. (Name not found in window) I contacted them and sent pictures but they could not find anything matching what I sent them. I am selling the home and I know that a couple of the guides on the sides of need to be replaced and at least one lock is missing. I know the inspector will find this so I would like to get ahead and get someone ready to repair. Is it possible to just replace the guides from this company with new guides from another company? Any other suggestions on easy ways to fix and what type of contractor should I call? The general handyman types did not seem to be a help at all.

I have a stucco home which got water damage where a blind is hung inside the window on both sides and at the top. The water damage came from an exterior leak from a window above and repairs to that will be completed when the rain stops. My question is how the edges of new drywall should be finished, assuming I can see how to attach it once I tear out the old damp drywall after the leak is fixed. I have read about tape on seams and drywall mud and tape in the corners of rooms but nothing about the edges of drywall where it meets other drywall with an outer corner instead of inner such as where the inner top edge of the new drywall will meet the vertical wall above. Which one overlaps, the vertical wall coming down with the new drywall nested inside it? And do you also put tape on an outer corner such as this one above the window? This will be my first attempt at drywall replacement but the house is for sale for much less than we paid for it and I need to do it myself. Thanks for any help or suggestions.