XK4 & Mark,
A couple of quotes from other sources;
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"Why can’t I use generic brake fluid in my British car? British brake & clutch systems use natural rubber components which are only compatible with vegetable based brake fluid. American brake & clutch systems use synthetic rubber components which are only compatible with mineral based brake fluid. The only vegetable based brake fluid commonly available in the US is CASTROL GT LMA.Use of improper fluids or mixing of fluids can lead to complete failure of brake and clutch hydraulics. Use of any fluid other than CASTROL GT LMA violates all warranty on brake/hydraulic parts.
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"All,
Check this out!!! Sent a note to Castrol website last nite! Got this back this am!!
Thank you for your inquiry. Castrol brake fluid, GT LMA is a DOT 3- DOT 4 with a glycol ether ester base which is considered to be synthetic in origin, although it is not advertised as such. Castrol GT LMA, which exhibits low moisture activity and exceeds the most severe performance and safety requirements, is the fluid of choice. For completely reliable brake operation, maintain the required brake system service schedule and use Castrol GT LMA Brake Fluid. The "scoop" is.... Lucas Girling is the brake manufacturer, and Castrol is "Girling Approved"."
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DOT 3 Glycol Based: corrosive to paint & rubber, highly water absorbant.
DOT 4 Glycol Based: corrosive to paint, does not absorb water as readily as DOT3, has a higher boiling point than DOT 3, can be mixed with DOT 3.
DOT 4/3 Glycol/Poly-glycol Based: Labeled "Synthetic" and "exceeding DOT 3 and DOT 4 specifications", it is still corrosive to paint, but highly non-absorbent of water, and has a higher boiling point than DOT 4. It can be used in systems having ABS, and can be mixed with standard DOT 4 and/or DOT 3 fluids."
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[ 09-14-2003: Message edited by: Dave Russell ]</p>