I have heard a lot of people talk about products that successfully remove rust but this stuff at only $1.19 for 2 litres seems to do the trick nicely.
I use it to clean all the screws and other pieces that need shining before they go in the polisher and also works great on pinball legs.
What is this amazing stuff you ask! well it is just plain old home brand white vinegar, soak over night and use a nylon bristle scrubbing brush to loosen the heavy stuff and bam!
Here is the coin door from Big Shot, it is not perfect but it is now usable til I get something better!
Cheers: Brettski... :)