Unfortunately Ken it looks like signs of Aluminium corrosion (white rust)

Probably water ingress under the paint at the edge of body to rubber strip. If it was me and I had the paint I would rub back treat it with rust inhibitor and then paint. The continue to get plenty of acf50 along the rubber joint regularly.

Hope this helps a little

Adrian

Buggered Off, to a modern none leaky car, heart's still ticking