Triumph Repair: Hydraulic Fluid Turned Crystalline, power microscope, hydraulic clutch

Question
Howard,

Belated as it may be, thanks for that diagram you directed me to on your website. (Engine: Re: Water hose connections.)  Though I saved the image, I appeared to have lost the email that would have otherwise directed me back to the link of my question.

As long as I have you on here, I have a question.  It's related to something curious I found on my Spitfire.

After sitting in the garage for 7 years I found the hydraulic clutch reservoir empty.  However, the fluid had changed from a fluid into a crystalline form and had overflowed the reservoir.  It was almost as if it had crawled out.  Looking at a piece of it with a 100 power microscope, I see that it is, in fact, crystalline in nature.

Have you ever seen this before?  And, if so, what causes that to occur?

Cheers,
George

Answer
I have been working on British cars since 1960 and have worked on many cars that have been stored for many years and I have never seen that, so I can't even guess what someone had put in there for fluid.
I always use Castrol DOT 4 in the clutch and brake.
Howard