First off thank you all for your insight. So today i started digging out the rotted wood from the end openings with a coat hanger with a little half loop bend... Was getting the wood out, but it was a tedious process...
After 45 minutes i decided to go another route. I slit the vinyl along the bottom edge. There's a groove so the blade went right along it. Once slit open, my wife lifted the vinyl up from inside the window. I was able to then get my hand inside and using a screwdriver, removed all the wood in larger pieces. The entire wood sill was wet rotted, nothing left of it.
Luckily the bottom of the jambs are in pretty good shape. Little rot that I'll hit with wood hardener.
Next step. . I'm figuring that now that I have access to inside the vinyl, I'll rip a piece of pressure-treated wood to the right size and slide it in, then with epoxy fill in any gaps.
Edit:. Added a picture of the largest pieces of the still...
