Oof, there is some real corrosion there. We face the same task; hoped to get it done this summer, may not. First decision is whether to keep the 1/8" safety glass, or change to acrylic (Plexi) or polycarbonate (Lexan). Each material has definite plusses and minuses. We're leaning towards acrylic.
Second task is sealing the opening. Our window surrounds have about 3mm exposed foam core around the opening. On the bottom and sides, at least, maybe all around, that core should be dug out and filled with epoxy -- preferably a good 1/2" deep, so the screw holes are filled. Six10 is your friend again.
Third task is deciding whether to save the weatherstrip, or see if a glass shop has the same kind in stock. It seems unlikely. It is okay, and perhaps better, if not. You can use double-sided glazing tape or, for the ultimate seal, sticky butyl tape to bed the glass.
Fourth, I think this is an opportunity to thru-bolt the frames, like they should have been originally. You could drill thru and then countersink the outer frame; or this may be an opportunity to swap port for starboard frames, in which case the inside (countersunk) frames become the new outside frames. Clamp, thru-drill about four bolts, install with acorn nuts, drill the rest. Remove & clean the frames; bed the glass in butyl in the outer frame; bed the frame in butyl to the cabin side. If changing to a thicker material like Plexi, some shimming of the inner frame may be required.
You can also just skip the frames and surface mount Plexi to the cabin. This has been done to at least a couple Ballads; definitely changes the appearance, tho.
I was literally speechless. It's safe to say I'm not placing an order for new windows any time this decade.
