The skins had split at the bottom of my doors where the aluminium and corroded against the steel door frame. The bottom of the frames appeared to be quite corroded too so I decided to remove the skins, repair the door frames and replace the skins with some better ones that I have on some spare doors with rotten frames.
Firstly I prised off the old skin using a screwdriver to lift up the lip of the skin. The rot was worse than expected on the bottom rail so I replaced it with a repair section bought off ebay. The rest of the frame was ok, needing only a couple of minor welding repairs. I cleaned up the rest of the frame with a wire brush in an angle grinder and gave it a coat of red oxide primer.
The other door bottom had similar corrosion to the bottom rail but only the flat section was corroded, the U channel was ok, so I drilled out the spot welds and replaced that section with galvanised steel and spot welded it on.
*If you weld with galvanised steel, unless you are using professional breathing apparatus, always grind off the galv in the area you are welding as welding zinc creates a poisonous gas that is very dangerous to your health if you breath it in*
Below is the finished door, needs another coat of paint.