Hi,
6 months ago I discovered small amounts of rust underneath my rubber seals on the doors. It's not a big problem at all but I wanted to squash it early.

Pulled the seals off and treated the rust with POR's 'Metal Ready' and then coated with POR paint. Had a look today and noticed the rust was still active and beginning to bubble under the POR15 paint.

What could I have done wrong? I've used this paint many times before but haven't had a problem with it returning.

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1995 E300 Diesel

You didn't do anything wrong. You just didn't do the job completely. POR15 seals the rust, it doesn't remove it. You need to pull the inner door panel and attack the rust where it begins. Scrape, wire brush and treat the rust on both sides of the door. You can use Naval Jelly (phosphoric acid) to remove the rust and there are numerous rust converters on the market to use next to convert the remaining rust. THEN you can seal it with POR15.

POR's "Metal Ready" works good also but you have to get complete coverage on the rusty areas whichever method you use.

Of course, FIRST you need to find where the water is entering. The usual suspect is the window seal.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Thanks Mike,

I'll take the door panel off and paint inside also. You are right, i think the water is coming from the outside rubber track that runs at the base of the window. The UV radiation is strong here in Australia and takes its toll on rubber(s). I priced them from the dealer only a few months ago but left it due to the high cost.

Not sure if this is something that the forum sponsor can supply but I'll try. They would fit nicely in a post it tube.

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1995 E300 Diesel

best way for those areas is to use penetrol after a good cleaning. Then clean your door rubber with soap and water and allow to dry completely, get hold of some real talcum powder (french chalk) and literally marinate the entire thing in it in a plastic bag. Most baby powders today are not talcum - so best get some real stuff from a tire bicycle or billiards supply store.

Install the rubber - then reapply to the whole rubber and specially on the top edge where there is a fabric piece - otherwise it makes a noise and can also rub away the paint on the cars body.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)