I believe the board would have to set a policy on the type of window allowed and then each home owner purchases their own.

There is likely a deficiency in the master deed language. A court would look at what is reasonable. It is unreasonable to not pull the windows to repair the flashing.....

So to follow, I would guess that the board can only state that owners have to put the windows back in a state that functions... 
 
Many things are possible in a special assessment and rule change process, but they may be forbidden from forcing you to buy their windows without a special assessment and rule change of the master deed and bylaws.

Having just gone through this in Hawaii, there are a couple of options. As suggested specs could be given to owners but the sills are still the responsiblity of the association. If as was our case, the water is causing damage to the common elements or to other units, the board has the right to make the repairs and charge the owners for the window portion. Lastly, some states allow the board to designate certain items as "high risk" if thier failure would cause damage to other than that particular unit. By doing this, the association assumes responsibility just as for other common elements. Plumbing is falling into this category for many projects.

Some sticky issues -- as a trustee/treasurer also in MA---- Since your docs define the ownership of the unit extends to the outer glass surfaces of the exterior walls, it would seem that the owners own the glass units and should be responsible for thier maintenance. On the other hand the faulty flashing would seem to be a responsibility of the trust. 
 
There could be a mid point wherein the association will pay for new flashing work and unit ownere, with some small help from the association, will fott the bill for new glass units.

We've had continual water damage in our complex since it was constructed, partly due to building standards that didn't require a moisture barrier at the soil line when they were built in the mid-60's, and partly due to watering practices (controlled by the HOA) that has allowed sprinklers to hit walls and windows for many years. In the most recent case, The HOA required the owner to replace the window to adopted standards, and the HOA was responsible for the framing,re-painting and any other touch up to the exterior despite the fact that our governing docs say very little about the split of such responsibilities in these situations. There was damage to both the window framing and the window (moisture accumulation between the dual pane window). The owner maintained the watering caused the problems and the HOA disagreed but there was no proof one way or another. I felt the HOA should have split all the costs with the owner for that reason, but I was in the minority on the BD. I'd really like to hear from others about any process they have to determine a fair share where governing documents are vague or silent. This has come up again recently with water damage (dry rot) being discovered in building studs when the HOA has undertaken extensive stucco repairs due to water damage. (Stucco repairs are a regular annual need.) The HOA has billed owners for the repair of building studs, which I maintain should also be split between the HOA and owners, since the causes almost certainly are originating from the exterior and from activities the HOA is responsible for supervising properly, like the sprinklers. To make tis situation more frustrating, we've just gone through an update of our CCRS and Bylaws and the BD chose to not address this area of responsibility. Any thoughts would be appreciated!

Bob has the right idea that the board has the right to make repairs. I copied (below) part of the Maintenance section of my condo docs. Your docs will probably have something similar. 
 
"d) The Association may, in its discretion, assume responsibility for any maintenance project which requires reconstruction, repair, rebuilding, conservation, restoration or similar work to more than one Unit and the cost thereof may be in the discretion of the Association either assessed against each Unit on which such costs were incurred or assessed against all Units as a Common Expense according to the circumstances." 
 
So the short answer is yes, the board does have the right.  
 
It is probably easier for the board to pay for the whole project as a common expense, because it is harder to organize for each owner to pay different amounts of money, and/or to coordinate separate installations. 
 
Here is an interesting question for you to figure out: For each unit in your complex, for this project, what is the cost of paying "by the window," versus paying by the usual percentage contribution for common expenses? Which owners benefit by each method, and by how much? 

I am having the same problem. I purchased my unit 3 years ago. They had sided my building 6 years ago. The contractor that they hired, did not put flashing under the siding. Until 2 months ago the gutters had not been cleaned, so when it rained, it came in. I have been telling the board about this for 2 years, via phone and e-mail.  
 
 
 
I now have aqpproximately $3500 in damage. When I called the president, he told me to get an attorney. My insurance company has their attorneys on the case. 
 
 
 
I have a board member telling me that it is an HOA problem. 
 
 
 
Do I have to pay for a new door, or will that be something the HOA be replacing? 
 
 
 
I live in NC and am disabled. 
 
 
 
One more thing, none of the units are handicapped accessible. Is he HOA responsible for this or am I? I live in the bottom unit of a 3 story building and will be on a scooter in the next few week.