MG Car Repair: Brake Fluid, rubber seals, dot 4

Question
In several of your answers, you have been emphatic about no DOT 3 fluid, and to only use DOT 4.  Unfortunately, the only auto parts store in my small town carries only DOT 3, except for a synthetic fluid that is rated both DOT 3 and DOT 4.  Is this acceptable for my 74 Midget, or should I look further.

Answer
Hi Corey,
Many aftermarket shop manuals claim you can use DOT 3 but I know from experience that DOT 3 fluid swells up natural rubber seals and on an old British car you have no way to tell if the seals in the clutch and brake have no natural rubber in them unless you replaced all of the seals and you are sure the new seals can stand DOT 3 fluid. As far as the specs of the two fluids DOT 4 can handle higher temperatures than DOT 3 so if for no other reason I still recommend DOT 4 fluid.
Howard