I won't know until I remove the cladding, but I'm guessing not because I've also noticed now that the wood on the inside of the bottom of the panel has bubbled out a bit. Makes me think the wood all across the bottom of the panel is in pretty bad shape.
Then rot might even have started running up the side of the panel if that's true. I have never tried to rebuild any of these, just replaced them. Is your rough opening a standard size i.e. 72" or a custom build? Because if that price you were quoted is for a standard size, someone wants to go on vacation.
With what you have posted, I would say your best policy would be to wait until the weather breaks before trying anything. March is only 5 weeks away! And if you aren't going to be at this house much longer, get a good vinyl unit. I'm not a big fan of vinyl anything, but I know houses with those units sliding well even after 20 years. And they don't rot. Sorry if that isn't much help.