Must be a bad week for windscreens! Mine fell out on the M6 as I trailered my new car up the road at the weekend! Where did you get your replacement and how much? Chesil don't post them. Tony at Pilgrim saved the day and is sending me one in a big solid box (fingers crossed Parcelfarce don't trash it). £99inc vat plus delivery.
Is the alloy frame not held to the posts by two screws? Is it them that are rusted? If so, you can either try tightening them a little first to free them off, or, drill the heads off them and replace them. I can e-mail you photos seeing as mine is now "sans" screen!
info@alastair-brown.co.uk