Hi everybody
Are you the original and only owner of the car?
If not it maybe worth trying to contact previous owners or dealerships to see what may have occurred.
I was going to ask the same
If the filler is there to fill a dent then there would be evidence of an indent underneath
If there is no evidence then could this be just a few layers of high build primer ?
Well, I think that I've got the reason why there is such a thickness of filler. I first thought that there was an oval reinforcing pad welded under the wing for the wingstay mounting. The left wing has exactly the same oval weld underneath it. After removing the side light and stay, I used a round file to clean out the inside of the wing stay mounting hole expecting to see below the filler two layers of aluminium, but alas no, only one 2mm thick piece (the filler at this point at the apex of the curve is 4mm thick)
So I surmise that the oval plate is flat, hence the filler being 4mm thick at the apex decreasing to 2.5mm at the crack to a normal micron layer on the superform wing.
I think the drawing simplifies it

The stippled area is the filler.
So why?
I'm the third owner so do not know the history, but there is no indication of earlier damage or repair.
The superforms were being fitted to 4 seaters for two years. It would be interesting to know if other cars of this era have the same configuration.
David 2001 4/4 4 seater.