Originally Posted by
markharrison
Without dismantling the windows, you can only see what you can see.
Usually rot in windows will be at the end of any cracks in the glass and the lower rail, probably in the joins to the stile which usually means the rail is also compromised. If there are multiple lights (aka panes) in the window frame, you will also need to look at the muntins.
If there was rot in the wedges you could just pull out, I would be greater than 85% certain the rest of the joint is compromised.
Then it gets down to what you are going to do about it. If you have the skills or the confidence to have a crack, they are probably repairable. Good luck finding someone to do it for you! That said, nobody is going to tell you doing this yourself is just going to be semi-tough!
I would also be looking at the sills near the stiles. I'd bet there are problems there too.
Post some photos and we will have a better idea of what is going on.