Glad you found the pins. I had a friend who did a brake job and instead of using the pins or the caliper bolts, he took the whole caliper apart, he finally called me when it was to late. Anyway, you booster could leak and all the other components could still be working. I know that on my car they are separate circuits so that you could loose vacuum for you door locks and the brakes would still work. I hope it is just brake fade. Try changing out all your brake fluid and door a good bleed job.
Henry

__________________
63 190d (sold)
69 220D (sold)
69 280SL (sold)
76 BMW 2002 (sold)
86 190E-16v (Demised at Laguna Seca Turn 9)
87 300SDL (sold)
87 300SDL 135k
87 300TD 280k (sold)
95 E320W 311k
95 E320w 180k
05 C320 4matic
06 E320 CDI 90k (Totaled by a texting 19 year old girl in a nissan)
2013 GLK 250 Bluetek 4MATIC 295k