Rob wrote:
I have installed upvc frames into new stone mullions. I am not familiar
with the
detailed internal construction of the frames but I have water leakage
from the frames onto the internal faces of the mullions causing damp
patches internally.
Anyone ever installed this type of frame into stone surrounds ?
Are there any sites which show how upvc windows are constructed showing
the carriage of water
through the frame and its disposal.

I think you're overcomplicating things. If the window frame is sealed
to the surrounding stone there should be no way for it to leak, and it's
no different fitting them into a stone surround than other types..
Other than that you'll probably find holes drilled from inside the
bottom rail of the frame to the front face of the frame, to conduct out
any pooled water from there?

Certainly there's no generic answer to your question as windows produced
by different manufacturers will all be different.

David