If you’re lucky, the whitening or ‘chalking’ may simply be heavy surface oxidation. In this case, a good polishing session should revive it. A heavy-duty cutting paste such as Farecla G6 may do the trick. Do it one panel at a time, finishing off with the lighter G3 compound then a quality, slightly abrasive wax polish such as Auto Glym Super Resin. Machine-polishing will make a quick job of it, but be very careful around corners and swage lines as the lacquer and paint will be very rapidly removed down to the bare metal. Test a small section by hand-polishing to see if it has the desired effect. If the lacquer appears to be degraded through its whole thickness, then a respray is, sadly, the only answer.