Re: Is it OK to use synthetic brake fluid instead of conventional brake fluid for the
...what's the real story on the Castrol LMA stuff? Is it silicone or synthetic or what?
It's a synthetic, glycol-based DOT 4 fluid, which is fine for use in your ST. LMA is just their marketing term for "doesn't absorb as much water as the stuff those other guys make."
Anything that says DOT 3, DOT 4 or DOT 5.1 is glycol-based; DOT 5 is silicone. That sounds confusing (and it is), but the 3/4/5 series numbers are more-stringent standards that don't dictate composition. Early DOT 5 was silicone; 5.1 is still technically 5, but they issued another number to keep people from damaging their systems by mixing the two.
DOT 5.1 will work in systems designed for DOT 4
only if you're doing a full re-build and have completely clean parts. Otherwise, if you've got DOT 4, stick with that. It's not going away anytime soon.
--Mark