Thanks again Tom for an informative and detailed report and feedback.
I have the SG and have checked mine this morning.
The substantial metal piece is all smooth and shiny on the outer surface (facing downwards into locker) over the complete length. I did notice that the inner surface (uppermost facing plywood top) was quite pitted at the open area exposed in the centre near the substantial upright post and on the open edge near the seat belt at the gangway, but smoother (by touch) away from these points.
I’m not an acrobat so I didn’t look up from underneath as in your photo for staining.
Guess that to take a good look it would be necessary to remove ply wood seat base top – a few screws and staples……if I was looking to clean out all the dust I would do that, or if you would like further comparison, I could be persuaded.
Cheers, Fred