Hi, John, as in oil I did mean an oil type inhibitors injected through the drainage holes but will be taking panel off to check for any further damage.
Update on sloshing noise!
just had Mot and inspector said that there was something dripping from door!
checked after Mot and found that drainage holes were blocked up and I drained 3 ltrs of water out of door.
I will be spraying some oil inside of panel to try and inhibit any corrosion!
Personally I would get a mild cutting compound and a random orbital polisher , give it a good going over and then use a good polish with the polisher and then give it a ceramic coating.