I know this has been discussed before, but I remain puzzled. The 15-year rebuild of my Mk 1 Sprite is finished, except that the master cylinder has gone rusty - again! First of all I honed out the brake and clutch bores, assembled the unit, wrapped it up and stored it away in the house. When I assemble the system I found the bores had rusted in storage. So I honed it again. By this time I was nearly ready to roll so I reassembled and bled the system, which worked OK. Then there was a delay with the clutch, so the car didn't move for about a month, by which time the bores had rusted yet again. It's now beyond honing so I am having the bores sleeved with stainless steel - which of course I should have tried before. This is a very difficult job as there is so little material between the bores, but my engineer says it's in progress. It will cost nearly as much as a new unit, but won't go rusty again.
Having had a discussion on this NG and elsewhere about brake fluids, I am using DOT 4 not silicone, so I'm well aware of the hygroscopy problem. But why is this not a problem with other vehicles? My motorhome sits idle for months on end and the brakes are always perfect. Why is the Sprite plagued with this? This is not new - I was honing master cylinders 20 years ago. Why are the cylinders not chrome plated? This would solve the problem cheaply.