Before you just start throwing money at a problem to "fix" it you need to diagnose it first.

Remove the nuts holding the master cylinder to the booster/servo. Slide the cylinder forward to inspect for leakage before you go replacing parts.

Have you recently added fluid to the reservoir and was an approved DOT 3/DOT 4 fluid, not a synthetic?

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now