Brake/clutch fluid

["Jeff McNeal" <jmcneal@ohms.com>]

Have I got this right?  The Castrol Girling equivalent here in the states is
DOT 4, right?  If I wanted to use silicone based DOT 5 instead (to protect
the paint when the master cylinder eventually leaks) am I going to destroy
the rubber seals in the brake/clutch cylinders?  When I had my first
Spitfire, I found out the hard way, but it's been over 20 years and my
recollection is hazy.  I don't want to make the same mistake twice. Thank
you.

Jeff