I have a 2008 Honda Civic that is currently leaking water into the backseat floorboards. We have done some diagnostics that have shown the seal on the outside of the window has separated from the window, and is allowing water to run into the door (and then into the backseat). I was hoping to find a way to replace this myself. Any ideas?
Do you mean the rear windscreen or the side door window? If it is the windscreen, I believe they are bonded in and so will be very difficult to do anything with unless you have specialist equipment.
If it is the door window, the seals on these usually clip to the door frame and so should be replaceable. You may find they you have to remove the window glass to do this, but the procedure for that ought to be oulined in the workshop manual (if you can still get hold of those for cars that recent)