One of the most difficult mistakes to correct is the Juan/Ahmal syndrome. While Juan and Ahmal are identical twins we might be pretty safe to say if you've seen one you've seen them all. Now I have a couple sets of identical twins in my extended family, and I can assure you similarity in looks is indeed superficial.

Problem is, people new to Volvo get this idea one 245 is just like another, and don't bother telling us what year, trim, transmission, etc. figuring they're all the same. But they're not.

Model years 75 to 90 had a pressure differential sensor (brake failure warning switch) to trigger the brake failure light. 91 through 93 used a float level sensor in the reservoir.

A torn seal in the master cylinder might leak out through the booster to be eventually burned in the engine -- a brake fluid leak well hidden from view. You'd have to separate the cylinder from the booster to confirm this. However there are many other places fluid could leak and not be noticed without a diligent inspection. You need to get your mechanic to do a thorough inspection to find the leak and fix it.
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Art Benstein near Baltimore

If you have any trouble sounding condescending, find a UNIX user to show you how it's done. -Scott Adams