Can I replace this rotten wood on a sash window

[hoagie007]

Part of the wood on the exterior of a sash window is rotten and some is missing, as seen in the photo. I can remove more of it with my finger but I don't think the entire length (height) will come away easily. The wood looks to have encased the glass.

I'd like to know if this is a quick fix? Can I clean up the rotten wood and simply glue replacement wood to the glass, and if so where would I get a piece of wood in such a triangular shape?

Thanks in advance!

 

[Jurassicspark]

Some wood filler will be a temporary fix.

 

[crank39]

That looks like just the putty has crumbled and fallen away, you can see the primed timber underneath it

 

[hoagie007]

Ahh so they use putty to fix the pane of glass to the wood? I should check out some other videos to see what they do. It doesn't have a wood like texture and as you say I can see the wood underneath.

I found a video and I'm confident now it's putty. Thank you very much. I have some linseed putty in the shed. I'll sand and prepare the wood and then add the putty before finally painting.

Thanks again!