What is your ultimate goal for the interior side of the windows?

Paint, varnish, shellac?

At any rate, if they were my windows, I'd seal that old dry wood up with penetrating epoxy sealer inside and out. And give them another 150 years + of life. I'd varnish the insides. For the outsides, I'd use a marine grade long oil alkyd primer, and then a couple topcoats of paint.

There are easier options to seal the wood up to. You could mix up a 50/50 mixture of penetrol and mineral spirits to quench the wood with. Won't work as well as a penetrating epoxy, but will work better than primer alone. But if varnishing the insides, I wouldn't go that route and use only the epoxy sealer.

The good news is the insides are already stripped. So they really just need to be sanded really well.

Without knowing what the windows look like, it's probably best to remove all the old paint and putty, sand everything really well, seal up with epoxy sealer, varnish the insides. Let cure. Flip over, add bead of putty and seat the glass. Install glazing points. Finish puttying. Let putty cure. Prime. sand smooth, 2nd coat of primer. Sand smooth. Paint.

For your first window, start with one in a non-conspicuous location.

The previous owners painted a lot of the trim, so even though I love the old wood, I think we are going to paint both inside and out. There are just so many more pressing issues I can't put the time into stripping trim to match at this point. I plan to remove and reglaze the sashes and install spring bronze weather stripping in the hopes that next winter we can cut down on some of the draft. Right now, so much of the glazing has literally fallen out of the windows, some are being held in by just the glazing points. Any wind and they rattle like crazy.

I'm looking at this as a possibility for the sealer you recommended: http://www.amazon.com/TotalBoat-Penetrating-Epoxy/dp/B00J36WRRG

So once I remove the pane and get the paint stripped and the wood sanded, I would just apply this all over the wood and let it cure, then once it's cured I can move forward with the normal reglazing process then paint once the glaze has skinned over, correct?

@ Sombreuil - Yes, this is also a factor in deciding to paint, some areas where there was water infiltration are bleached or stained and the wood may not take a stain well or evenly ever again. This is one of the worst.

I'm not sure what TotalBoat stuff is.

Seriously, being a no VOC product, I'm not sure how deep it will penetrate into the wood. Water based resins are bigger than solvent based. Unless something new has been developed...

The only product I have experience with is Smiths CPES.

Others seem to like Abatron.

I wouldn't stain the windows.

Another good resource is:

http://historichomeworks.com/forum/viewforum.php?f=16&sid=416005554e4025b6f2caa6e88007e09b

I've used the boiled linseed/turpentine mixture on all mine. Several looked like yours. Dry. Any bits of shellac long gone. It's like giving your wood the drink of fluid it's been needing for years.

I highly recommend it!!

Could someone share the mixing ratio for the linseed/turpentine mixture, please? I also have very dry sashes and sills and would love to try this.

It is a 50-50 mix of boiled linseed oil and turpentine. It really makes a difference with old wood. I have a not-so-old picket fence with horizontal cross pieces that would not hold a paint job. The paint would be cracking in less than a year. I used the blo/turp on it and it has been holding the paint for 3 years so far. I use it on all my windows. For more on this stuff, google the word "blopentine."

Awesome, thank you so much for sharing!

And of you add 20% Flood Penetrol it speeds the drying a little. has anyone tried this, I have?