With all the talk about weatherstripping, here and elsewhere, I don't understand why there isn't more mention of the interlocking kind. It's original equipment on my 1913 windows and have heard mention of it here, google it successfully and it is the best thing I've ever seen or heard of. It's exactly what it says - interlocking. There's a folded piece of thin metal (zinc?) nailed along the length of each side of each sash and the stops. The top and bottom sashes interlock and slide up and down inside the strip on the stop. There is also interlock on the meeting rails and at top and bottom where a folded strip actually fits into a metal lined slot on the top/bottom of the sash. There's no way wind can penetrate. I don't know why it's so hard to find photos rather than drawings of them but if I ever get back to restoring windows I'll try to remember to make a point of posting a photo here. I have ancient triple track storms on most windows - I've only been able to find an old storm for one of my 28-30 windows (don't remember if I included the two attic windows in the original count) and no clue when they can be replaced. How old are they? How long does it take for aluminum to rust? They are heavy and tight, though and the combination produces no frost, no condensation, no air movement. I visited a neighbor who had just had "top of the line" replacements installed and could feel cold and plenty of air penetration (an honest to pete breeze.) I tried not to be too visibly smug but it redoubled my commitment to my old windows. Here is a link that might be useful: the best illustration I found

Thanks so much for your reply and suggestion! Will epoxy prevent leakage? We believe the hole, no bigger than an inch in diameter, diverted appropriate a/c drainage - and caused water damage to downstairs unit.

I have no experience with PTAC or this company. I found them and offered it as a suggestion. The equipment you have is made by Trane. I am not sure what equipment they sell. This type of equipment somewhat specialized. Therefore it is important you find an installer who has experience installing PTACs. Perhaps they would be willing to provide a reference of someone who lives in your building. Here is another PTAC installer in NYC if you want a second quote.

A few years ago I had my windows and entry door restored in my 1100 sq. ft. 1928 house. My goal was to make all of the windows easily operable, to repair dry rot (one window sill), to restore the original divided light door and hardware, and to maintain the architectural integrity of the house. I don't recall the cost but I think it was under $10k. Consider, though, that I had fewer windows than you and the scope of work was different. Most of my windows are easily accessible from the outside, and there are no screens. All work was done onsite rather than in a shop. The only weather stripping was for the front door. New latches were installed where needed. The work did not include any painting. I was home to observe the work and I was impressed with how labor intensive it was. It took many days of focused work to complete. This is specialty work so not cheap. But replacing my old-growth windows with new wood windows would have cost much more than restoration. And I couldn't bring myself to install white vinyl windows in my little English cottage. That said, I live in a relatively mild climate (Pacific Northwest) that only occasionally experiences extreme weather, which might not be your situation. Most of my neighbors have chosen to replace rather than restore their windows, so I'm definitely the odd one on the block. Good luck with your project.