Solution for fixing rust spot at corners of rear W123 windows?
 

Folks, my 1983 300D has the classic rust areas at the bottom corners of the rear window, you know, the spots where the paint bubbles up and rust forms at the corners of the window, right outside the seal? I have a bad one on the passenger side, and one that is starting on the driver's side. I know that the real, long term solution is to remove the window, fill, sand, paint, and reinstall the window, but I don't have the resources to do all of that.

Does anyone have a good intermim technique for sanding out the rust hole, then filling it with womething, sanding it down, and repainting? Thanks so much in advance!

I'd suggest POR-15. I have used it a few times. My local Car Quest sells it in a pint or quart can. I buy the smaller six pack size from the maker. Wire wheel off the rust as much as possible. Clean the metal. Paint on two coats of POR-15. Then primer, then your color coat. POR-15 usually takes about 2 hours to apply the second coat and 2 hours to apply the primer. It has to be a bit tacky to apply another coat. I don't know how far back the rust is under your cars seal.
Tom

Thanks so much, Tom. What is por-15? Is it a rust converter chemical, or is it a body putty? Thanks so much again for your help!

POR-15 is actually like 'super glue'. You use it like a paint. It comes in a couple of different colors, black, gray, silver and clear. It doesn't do well in sunlight thoguh. So you should cover it with a primer, then paint. There are other rust stoppers. I think Eastwood sells another one. POR-15 doesn't convert the rust. It basically encapsulated its. No air, no more rust. It dries hard. I've had it on the brake drums of a car since '87, no rust. It haven't driven the car much though. Wear nytril gloves and I use a foam brush. I bought the small cans of it last time in a six pack. After opening, I put a piece of saran wrap between the lid and the can. Helps seal it, and keeps the stuff good.
Tom
PS, they do make a body putty.

Thanks so much for taking the time to share this with me! I will definitely look for that stuff. I'll make a few phone calls to see who carries it here in Houston. So, do you agree that my process should be:
1. Sand/grind down the areas of rust that I can see
2. Use the POR-15 like a sort of paint, let it dry well, then prime it
3. Use some sort of body putty/filler to fill in the hole
4. Sand/grind it down until it is smooth.
5. Prime the area
6. Find the correct color of paint in a spray and spray paint the area

Any other help or advice is GREATLY appreciated!

By the way, any suggestions as to where to find a small spray can of paint that will match? I believe the color of my car is called "midnight blue" - it is a very dark blue, and many people have thought the car was black.

Thanks so much again!

Just wire wheel off the rust. It should get it down to surface metal. PRO-15 actually stick better to rust than bare metal. They make a prep for bare metal. Spray on the primer befroe the POR-15 dries, about 2 hours depending on humitity. If any rust holes, then fill in with some body putty. POR-15 makes some type of epoxy putty. I have some, but never used it. There is an online place for spray cans of MB paint. I don't have the address saved.
Tom

Automotive touchup.com is the site where I got color matched paint in spray cans.

When using POR-15, there is a cleaner and a metal prep that should be used prior to the paint. The metal prep helps to kill the rust and dries with a zinc oxide coating that allows the paint to adhere better. If you don't seal all the areas of rust it will keep coming back. If the rust is under your window seals, you may be wasting your time trying to repair without removing the windows, plus if you get any POR-15 on the seals they will end up fused to the body. I am fixing rust on my wagon quarter windows, and it is always amazing how much more rust there is when you start scraping and cleaning. I have to remove the windows on both sides and I am using POR-15 to treat and touching up with color matched spray paint (base and clear coat).

Good luck and you can order POR-15 online:D

http://www.por15.com/