Hydraulic cylinder treatment?

[Bruce Parker (RIP)]

My "now sitting on the workshop bench" dis-assembled clutch slave cylinder (Bendix 76988) had a bunch of thick brown fluid on the 'air' side of the piston. No amount of regular bleeding/fluid replacement would get to that so off it came. My first look in the bore gave me sweats. But I see most of the 'rust' was congealed fluid that is coming off quite nicely. Heat may be a problem, but even the little bit of fluid finding itself past the seal is sitting on the bore and I may have to resign myself to that being a semi-annual maintenance item. The accelerator and clutch master cylinders have fluid on both sides of the pistons and that fluid is clean and can be replaced. little chance of rust here. I hope.