KB1ESY. Your 320 grit is too coarse. You should follow up with 600A wet-or-dry, using water as lube. If smoother finish is desired, switch to 1200A. Best results are obtained using several finer grits. Going to extra-fine in the beginning will work, but will take forever!
Sounds good! I used 320 because it was the finest I had in the toolbox. Will order some finer grades and have a go.
Among other things, the sandpaper has largely removed the existing finish (the gentle, directional "grain" that these Bud chassis have when they are new). So I suppose the trick now is to use very fine sandpaper to eliminate what is left of that finish as well as smoothe out the striations caused by the 320-grade. There are currently two issues after my initial cleaning effort on the T/R switch: (1) striations caused, as you point out, by over-coarse sandpaper and (2) patches where a bit of the original Bud finish is still showing, and this contrasts with the nearby patches where it has been removed altogether.
I can see that using very fine sandpaper could take forever, but the patience would be well rewarded if the only other options were to either "live with it" or rebuild using a new Bud chassis!
Edited to add a question for BSU: Even with the very fine paper, should I continue to sand in only one direction? Or should the ultimate aim be an even finish with no visible directional grain, in which case I would assume a gentle rotary motion might be used at the end of the sanding process, with the very fine paper?
73 de Martin, KB1WSY