Is it possible to replace original vinyl windows with retrofits

Andrew, excellent question and great photos. The problem is a bit complicated. I can see from the photos that the water migration is coming from the top, perhaps even above the top of your window. Anytime the plaster separates from a concrete base, it means the moisture is coming through the concrete, most likely from the out of doors in your case. Unfortunately the proper fix would have to be diagnosed and repaired outside at the source of the leak. Since you have no assess to the outside to explore and repair, the only mitigation to the problem from the inside would be to seal the concrete with a hydo-seal product such a Dri-loc sealer. I really think trying to replace the scratch and finish plaster coats will be a waste of time and fail again soon. I would strip away all the plaster to bare concrete in the effected area, making a clean line at the end of the bad plaster. Attempt to dry it as much as possible with a fan or fan forced heater. Something like a small box ceramic heater would be fine. Strip out as much of the caulking from around the window frame as possible. Paint the concrete with two coats of the Dri-loc sealer. Let it cure completely, recaulk the window frame with a Silicon/Acrylic paintable caulk. Paint the sealed surface with a recommended type of paint compatible with the sealer you select. You will not have as nice and smooth a surface as the original plaster, however, since you cannot stop the source of the water, the goal here is to simply stop it from entering your window bay.

Since the original window sash, and not the jamb, were replaced with a window replacement insert, to keep the look the same, you need to do some fabricating.

All this is dependent upon if you can find an exact replacement unit to match the one installed in 2007. The chance of that.... maybe. Window manufactures make changes to their product over time. Your window is possibly not in production anymore, but the next generation of window that carries the same size and some the details is what would now be available. Again, this is only a possibility.

What you will need to buy in addition, and this will be much, much more unlikely, is the wood window unit that matches the original one to the house when it was built in 1991. If you do, you would still need to throw away the operable sashes of that unit and install just the jamb. A big expense just to throw away a major part of it.

If it were me, I would get the materials to make a new wood jamb to match the one installed in 1991.

Construction details for wood window jambs are really quite basic construction. A tablesaw and miter box is all that is needed for tools along with drill and screwgun. Priming everything before assembly would be essential.

The brick mold on the outside of the window may be the only other part difficult to match exactly. All are basically the same size, but there are minor detailing differences from one supplier to the next. Some folks don't worry over this too much since the differences are so small.