IMHO any paint thats still firmly adhered should be left on, (assuming its the original paint and not hammerite
) It will be a good base coat for your paint job.
thoroughly flat down and degrease, and use a wire brush in an anglegrinder/drill to remove powdery corrosion, before flatting the bare metal down with 220 or 180 grit. then you can get aerosol acid etching primer in halfords, treat the bare metal with this, then give a coat of aerosol high build primer to fill any pock marks before flatting that off. then recoat with primer ,Then paint on your top coat.
did this on my leg and its stayed on OK!