window leak

If I understand your post when you took off the inside window trim you said you saw water running down from the top corner all the way down to the lower section of the window from the inside of the MH is that correct? If so water is getting past the butyl tape around the outside surface of the sidewall. With the inside trim removed I would have someone run water from the outside top corner while you are inside to verify where the water is leaking in. There is roughly a 1/2 in flange that makes contact with the sidewall to seal the window. Sometimes if the window opening to cut out too large or uneven that surface contact area my be a lot less. On my Georgie Boy they did not use a template to rout out the opening and it was not much sealing in the upper corner. Just look in the upper corner and see how much of the tape you can see. If you have very little contact in that upper corner area you will have to remove the window and shim the bottom and side before sealing with the new tape.