What are the possibilities for restoring sunlight-discoloured pieces? There's dilute hydrogen peroxide for white pieces, but how about grey and blue, which are the other two colours where the yellowing's most noticeable?
I wish more pneumatic models had used an air tank. Why didn't they? They cost implications are surely fairly slight, and on more recent larger models there has certainly been space (and it could be made to look like a fuel tank on a truck).