But modern 'roller skate' cars won't really have filler used during production will they? (save the odd bit on a ding or two maybe)
With comments like that I'm beginning to understand where your 'plantpot' reputation comes from. It's a valid point - equipment (such as it is) is readily available.
But it does shrink sometimes. I've got one vehicle where the PO had rear wheel arch repairs grafted in, at certain angles you can see, what looks to me, to be filler shrinkage. I'd love to strip it back to metal and have a go at lead loading it but suspect It would end as a balls up.
Julian.