i find it really odd that seat would put a clearcoat over a non metallic basecoat, usually the laquer/clearcoat has UV inhibitors, that prevent fade and is normally used over metallics.
it would be costly for seat to use this method on a solid base coat, partly why you pay more for metallic out of the show room.
if your paint is looking slightly white,very pale this should just be oxidation and UV bleaching on the surface and can be removed by polishing.
did a bodyshop tell you it can only be resprayed? in some cases it can just be to save time, a flat down and once over really doesn`t take long.
i have mopped my friends yellow leon cupra and got good results
for what it costs for some G6 and polishing cloth it would be well worth trying, i`d also recommend the black finger sponge from Farrecla also its nice and soft.