I've had the T5 since new and I still think of as new but it will be 20 years old in January! Sills almost never rust through on T5's. Mine was the result of crush damage which happened at six months old which was hurriedly repaired (not by me!) and rotted out after ten years or so, By the time I had dug it all out with a screwdriver the full extent of it was pretty shocking, 
Good luck with yours.
Good luck with yours. 