It looks like one of the foam blocks that sits on top of the wing at the end - to stop wind noise, which reminds me as I need to buy two due to mine coming loose and getting soaked!

The part numbers are LR023472 (left hand) and LR023473 (right hand)

Take a look here for location - https://www.fullfatrr.com/forum/post472154.html

I'll be buying two now I think to try and fix some excess cabin noise!

They soak up water and create a lovely environment for rusting sills etc  Gone to a good home: 2011 4.4 TDV8 Vogue SE Buckingham Blue with Ivory and clear glass = "Rory"
2025MY Defender D350 90 in Silicon Silver on coils
1974 Series 3 Lightweight = "Millie"
Many, many other Landies over the years
My preferred specialist: www.glenrands.co.uk
--------------------------------------------------