Vinyl siding issue......
 

Have a leak after getting new windows installed. Ive been able to
narrow it down to what looks like the fact that wind-driven rain (we
dont get the leak in a normal storm with no wind) is pushing water
underneath the j-channel of our vinyl siding where it meets a roof line
above our breezeway. This also happens to be right above the window
that is leaking, so we have the intersection of a window, roof, and
eave/overhang.

After looking further, I noticed that the j-channel used to finish off
the siding where it meets the roof has no flashing behind it. So my
guess is that the water is pushed under the j-channel then running down
the roof but against the original clapboard siding, then running along
the clapboard and into the house (the water comes in *behind* the new
window).

Question is - where should I put the flashing? Should I remove the
j-channel, add the flashing and then reinstall j-channel? Or can I
bend flashing so that it kind of sits in the j channel behind the
siding and then the rest covers the j-channel? Obviously (if you can
understand my weak description) the easier fix is to rest it in the
j-channel, but Im thinking the right way is to get it behind the
j-channel........my only question at that point is should I pull the
shingles off the roof and have the flashing underneath the shingles?
Or just rest it on top of them (basically come out from underneath the
j-channel).

Thanks!
-Chris