Hi Dave!
Happy New Year to you and yours! And of course to the rest of you FGers out there.
I use panel lines and rivets drawn on the textures. Right now I generate a standard and inverse layer of combined lines & rivets, and shift the underlying (white) layer 1x1down and then left / right depending on the surface's direction (essentially going back 1 px from the front of the aircraft to the back. I combine these layers after moving the underside white one. I set opacity to 25% (generally). I also use a copy of the combined textures layer to derive dirt accumulations associated with the panel lines, using first a motion blur (directionally shifted), then a gaussian blur to fuzz things up a bit.
For the aluminium layer I use a standard "metal square" image I have and transfer its size to fit fuselage, wings, stab, etc. I use (in Photoshop) the warp transformation to bend the rectangular chunks around the space of each bit. Finally, I select random panels (using the panel lines as a guide) and adjust brightness anywhere in the range -15 to +15% to five a non-uniform look. I like the look this gives to bare metal a lot! Special nod: noticed this look first on Gooneybirds livs, which is my personal standard for excellence!
But back at ye, Dave.... When will we see the Lockheed S-3B Viking in all it's glory? I'd be happy to assist in painting....
Best,
G