This is a recurring question about the Type 3.  I have posted some pictures and information to help find and clean out these important, but simple, elements of the Type 3 door.

There are two drain holes in each door.  One at the rear bottom corner and one at the front bottom corner.  The hole is actually punched in the door inner panel as shown in the cross-section of the illustration below.  The first photo shows a close-up of the rear drain hole.  I have highlighted the hole in red.  The other two photos show the location of the rear and front drain holes respectively.

These holes are important since the window scrapers on the outside of the car are better described as water deflectors than seals, contrary to popular belief.  The inside of the door is designed to be wet!  The problem comes when the outside scraper is old and cracked or pieces are missing.  Leaves, dirt, pine needles and other stuff gets inside the door and clogs the drains up.  The bottom of the door stays wet longer and the dirt holds moisture and promotes rust.  The bottom of your doors can literally rust from the inside out.

So, pop your door panels off and clean all the junk out of the bottom of your doors.  Use a wire or tie wrap or something long and skinny to make sure the drain holes are clear.  I wire brushed the inside of my 66 Squareback doors, vacuumed everything out, and then painted POR-15 rust preventative paint inside the bottoms of the doors.  Just make sure that if you paint the inside that you do not block the drains up with the paint.  The POR-15 is nice for this since it is very thin and will just run out the drain holes leaving a nice coating behind.

When you reassembly the doors, do not forgot the thin plastic sheet between the door and the door panel.  Remember the inside of the door is designed to be wet.  The thin plastic sheet keeps the fiberboard door panels dry.