Thanks for your reply, craig.
yeah, i have one of those thingies. I'm a lot embarrased that I looked in a manual instead of taking a good solid look under my hood. I have a power brake booster, all right. Mine IS leaking fluid - I can see it leaking from where it joins the master cylinder. But it is a tiny trace leak, as I check my brake fluid routinely and have had to add very little.
I find I have to step hard on the brakes, but the car actually does brake pretty well. As I step on the brakes, I'm starting to hear the faint sound of escaping air pressure in the driver's compartment, a sort of "ffffffsssssshhhhffff sound. I'm trying to decide if I need to replace the master cylinder, the brake booster, just a seal, or even just bleed my brakes. what do you think

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Love driving my '77 450 SEL!
124,000 miles