Being 40 years old, I guess it has earned the authority to begin flaking off. Just never heard of this happening.
I would power wash the area well. I would then get off all the stuff that it would not remove. I would then prime the area. I would then "spray" paint the siding on a calm day. I would use latex exterior Sherwin Williams or comp. paint.
This should do it.
The spray method was mentioned, because it will give a more cleaner paint look finish. Rolling or brushing will leave those strokes.