ALL 914 parts now have surface rust. Even NOS stuff has rust now. If you know how to treat and stop it it will out last you. If I were closer I would gladly give you $ 200.00 for that lid. The 6 I purchased from California had rust through the rear lid above the latch. It happens. I purchased a lid from a car in Vegas. I'm picking it up when I get out west.
If you fixed rust holes in your lid with lead your asking for it to blow up in your face. There is a big stupid piece of foam in the cavity above the latch. The heat required to tin the metal and blend the solder is plenty enough to cause oxidation to start forming. Any thin metal you didn't find are now on an accelerated path to failure. Did you get a year or two out of that repair? you were lucky.
Here's how you treat the inner structure and inner lid assuming you have no holes. First use a scraper, piece of sheet metal, sand paper or anything you can get to scrape loose any scale you can get to between the inner structure and outer lid. Wash the area out with your favorite rust converter. Be sure to neutralize the converter and use heat to dry the lids inner structure. Media blast the part to remove the paint and surface rust.
Purchase Eastwoods rust encapsulator in a spray can.
http://www.eastwood.com/rust-encapsulator-...ce-aerosol.html This product has an awesome spray nozzle that fans the product as it sprays.
Mask the gap all the way around the inner structure to seal the space. Use the hinge, latch and bump stop holes to inject and flood the encapsulator into the sealed space. It's thin enough to seep through the pinch weld flanges.
I have used this method on lids with surface rust showing. The key is to take your time and get the scale off as good as you can.
Rick, Thanks so much for your clearly written and well thought out reply. It really is this sort of field proven well thought out information that helps so many of us here.