Rescued the bits from the vinegar before work this morning, by emptying the container.
Didn’t get a chance to then clean / dry then until after work.
Big improvement all round.. the small bolts and washers showed the best improvement, but the brake arms did well too.
Started the process of fitting it all back together, and only realised there was a spring in the brake lever when it fell out. Took a while, and the dismantling of the other brake lever, to work out its orientation, but got there in the end. I booked a day’s holiday tomorrow, for a big ride and some more tinkering!