brakes continue to hold for a few seconds after release of break pedal

sounds like a case of contaminated brake fluid...take it to a brake shop and get your brakes bled properly with fresh fluid~...please.

Agreed. This same problem could turn from brakes holding to brakes failing. We are talking life and death serious ...any master cylinder issue is

feel like those two chipmunks who say "after you" no "after you" Mr. Hutch~H25~

Personally have had varnished brake fluid with my SINGLE cylinder 59 salmon colored Catalina with rusted/non functioning parking brake....hey, I was just a kid, though the 389 had 68,000 miles on it before a rented Dodge aries K car (what came out a rhombus) decided to set it non- driveable---the motor was quickly sold, lawyer took all the money.~

you scrub it against the curb till it stops~....solution for NO BRAKES...and NO PARKING BRAKE~

could be one or more of these suggestions: sticking calipers (piston not retracting) slide/ guide pins freezing up, primary and secondary proportioning valves in the master not working properly, or brake hoses collapsing internally.