Duraglas Repair of Window Sill

Last night, I took out the old single pane wooden picture window (48" x 54") to see what I'll be up against when I install the VRW picture window this weekend.
In one lower corner where the old aluminum storm window must have leaked, I have some rotten wood. It's rained the last few days, but the area is dry, so I don't think the storm frame that I installed 5 or 6 years ago was the source of the leak. I'm pretty sure it must have been the old frame which was in pretty bad shape when I removed it.
Replacing the entire sill would be a major job and as far as I can tell there is only this one spot where there is rot.
I replaced the double hungs on both sides of the picture window last year and there was no sign of rot on the sills below those windows.
So, I managed to poke away at the rotten area and got down to solid wood on all sides of the rot. My plan was to use some Duraglas to fill in the area and then prime and paint it.
It should be noted that this area is interior of the external window stop so it will be completely covered by the replacement window, which will then be sealed with caulk along the seam of the exterior stop and the window. (There was no caulk used with the old picture window, so I'm not surprised that water made it's way under the window)
Anybody see anything wrong with this type of repair?
Thanks!
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Sounds like what I would do also.
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