There is a problem with a few casement windows on the side of my house.
During window-driven rain, they tend to leak water from the top gap where
the window shuts. These windows generally don't shut very tight at the very
top (either due to not being well-aligned or maybe being warped.) I'm
wondering if this problem is generally solvable by replacing/enhancing the
rubber seals/gaskets rather than having to bother replacing the entire
window.

There are two types of seals that likely could use replacement:

1) There is some type of rubber seal on top of the window frame (the one
which holds the glass panel) and it is works a flap that is supposed to
point upward and make contact with the top of the outermost frame when the
window is shut. It seems to me that this is the most important seal to
prevent water leakage.

2) There is also a rubber gasket around the entire perimeter of the inner
frame which the window's frame presses against when shut. This gasket fits
looks like it is attached by flap that fits within the grove within a
groove. Other than the flap which sticks in the groove, it looks sort of
like a rubber tube.

If the leak is coming from the top gap where the window shuts, then could a
window-repair expert easily solve this by replacing the seals, or is
replacing the entire window my only option?

Thanks.

J.