Great story, I love the colour of your car.
Here in the UK we just change the whole slave cylinder when they are leaking like that as it's normally down to lots of rust ruining the sleeve allowing the brake fluid to get past the seal on the piston in the slave cylinder, the rubber covers on the ends are only to prevent dust and dirt contaminating the piston as it comes out of the cylinder.
I hope your mechanic sorted out the leak and didn't just change the rubber covers!