@Plimpington2, I think it wise to wait for a cleaner example. This is not a model to gamble on a rough one, hoping to return it to full glory. I expect that if switches and pots have internal damage (as well as solder connections, leads on semiconductors, and even wiring harnesses) then you are just asking for ever ongoing intermittent problems that will be impossible to fully chase down and correct, in practical terms. The time and money spent trying to correct such issues will quickly run you beyond the cost of just buying a really nice one to start.
I've been down this road once, having bought a JDM AU-555A and QS-1 as a bundle (from a shop in Japan). They arrived in original boxes, and worked passably well, but were heavily corroded inside, and on the steel chassis and rear panel. Oddly, the aluminum bits (front panel and knobs) were undamaged, but filthy. Those cleaned up nicely. I eventually set the 555A aside as a parts unit, using the knobs, button caps and a few other bits for improving other components I had in the same series.
I eventually found a domestic QS-1 on the cheap that had been partially parted, but was in perfect cosmetic condition, so made a good unit out of the two, and the rest got put aside with other parts units I've retained. I'd like to find a clean 120V 555A, but it isn't a priority at this stage. I dont think I'd knowingly buy another component with this kind of corrosion present, unless it was dirt cheap.
