What're my options to restore the cap on this 100 year old window? And, is that top wooden piece called a flashing?
If I want to simply replace that flashing and caulk, does that it simply slide in and out, once I remove the nails? Or is there more to it?
The top trim piece should be sloped to shed water away from your siding.
It is then nailed in from the top to the window casing.
Grab a small pry bar and try to get it in between the casing and the trim piece; you should see nails.
One way or another you have to remove it; you may opt to break the trim into pieces.
If this seems impossible then that first layer of siding should be removed first.
If you replace it then opt for PVC to avoid future rot.
I tentatively agree that @MonkeyZues provided a good solution, but it was not as straight forward as implied.
First, the installed drip cap is mechanically held in place by a lip that tucks under the siding above (see example below): simply removing nails was not sufficient to slide it out. To extract all of drip cap, I had to remove either the siding above or window header below. On top of that, the size of this OEM drip cap is no long stock material at home supply or moulding centers (local or online). What is available is the right shape, but not the right size. For my 100+ year old house, to replicate the OEM drip cap (which had disintegrated its extraction), it had to be fabricated from scratch.
While I was able to make a replacement part, install by removing the window header, and consider it a "proper" solution,...I would NOT recommend it as a "preferred" solution if the drip cap can be repaired.
In this specific case, @MonkeyZues is right, the drip cap was in terrible shape and needed to be replaced, but it came with the risk of having to remove and reinstall 20ft span of siding, which is not manageable with one person and one ladder. Which is why on another less rotted drip cap, I simply restored with rotted-wood restorer and wood filler and many new coats of paint.
