When I removed the trim around window I used LPS 1 as a lubricate to ease removal; most any lube will work.

Window and gasket removed and installed as a unit with the plastic tools I made reference to in prior posts. You reseal gasket to the vehicle with bedding compound and reseal the window to the gasket with the same product. Install window with gasket on it to vehicle.

I would think your gasket could be reused once it's cleaned up. I used pressure washer to blast off as much old bedding compound as possible and then used 3m general purpose adhesive remover to remove the rest.

Of course it would be a good idea to repair rust damage that caused leak before you reinstall window.