It was never a problem in my 67 wagon, so I assumed that problems with the hydraulic clutch were fairly uncommon.

However, it was late last year, when the clutch reservoir in my 68 was completely empty one morning. After refilling, bleeding and running for a couple weeks, I had the same problem and then I found leaked fluid on the firewall. I ordered a rebuild kit for both master and slave cylinders and successfully rebuilt both.

Things were fine until a month or so ago when I found fluid leaking out the slave cylinder. This time I pulled the slave and swapped on the cylinder from my 65 cabriolet/parts car.

Things were again fine for a couple weeks, but I've again found my fluid vanishing. NO obvious leaks from the MC this time, but I've not dug around much.

So, this brings me to my question.
What the heck is going on? Why can't the cylinders keep fluid? Are the rebuild kits inferior? Do the cylinders score that easily?

I'm not too keen on the pricey new master and slave cylinders - especially when I have a box of cores. I've read about Ron K's o-ringed plungers - does that solve the problem or is it just a good precaution?

What is happening and why do these things keep failing?

Thanks as always.