These are old codes, and bear no resemblance to the modern ones. All you can do, is find some original panels, and paint match them. Dream Machine will do a perfect job, but it won’t be cheap!
The shaft the gear lever is bolted onto? See how far in and out you can push/pull it. If it’s more than a few mm, there’s your problem, as1460 says. Easily fixed.
Problem solved almost immediately, Andy! You going to stick around long enough to introduce yourself in ‘General’? Maybe post a few pictures, bit of history ect? And welcome.
Phosphoric Acid is a good rust remover. I've used it a few times in the past. Dilute 1 part acid to 4 parts water. Brim the tank, and let it sit. When you're happy, rinse out with water and baking soda to neutralise the acid. Dry asap. It leaves a coating that won't rust.
Black treacle (Molasses). Mix 1 tin with 1 gallon of boiling water. Takes a while, but won’t damage paint. How about Electrolysis? Washing soda, battery charger, bit of sacrificial steel and away you go!
Robert’s your Mothers Brother!
No! You’re not alone! Little bit at a time is the way. If they’re old bolts, they really need renewing from time to time. They eventually become brittle with the heat cycles. OE aren’t cheap. High tensile Allen’s do the job.