Brushing the little bits
At this point I started rechecking the instructions for what actually were the bits to be painted metallic after I had already blasted the whole thing green. Off the top of my head I remembered that the cylinders of those two cans (but definitely not the lids) in the carriage's front were to be painted, in addition to a couple of other small pieces. But of course I was wrong.
The hydraulic cylinders had the lids on the painting list, as were the weird tracks on both sides of them, and a set of rails and stoppers framing the ramming device. The handles to control the setup's elevation were painted as instructed, as were the handwheels for the elevation for the gun barrel itself. Though unlike what the Revell folks wanted I only painted the outer rim and left the spokes green, as I expected to be painting them some other colour rather soon. As you could see below, the setup was already looking a bit dazzly for a weapon of war and I didn't even follow the suggestion of painting the gun cradle's axles metallic. Just to see how it worked I only painted the innermost part and even that seemed a bit weird.
Round 2
After a good night's sleep. I felt that it was way too blingy and more like a beginner's first Warhamer 40,000 tank or something, all it lacked were a few dozen skulls and shit. Still, I did an image search and quite a few finished models looked just like the instructions wished, but especially the hand wheels looked like they had been lifted off of a clown car. The parts that were to remain steely I was going to drybrush with either of my duller/darker metallics, so that they wouldn't stand out quite that much, as if the device was fresh out of the factory.
So I repainted the handwheels, the inner ring of the gun axles and a few sloppily painted overflows. It was noticeably better this way. On the handwheels painting over the metallic was a bit less covering than perfect, but maybe it'd work as paint being worn, just done the opposite way than usual.