It is possible for a piece of the inner rubber lining in a brake hose to pull away and act as a "flap" valve. This can happen in older brake hoses and result in either pressure not getting to a caliper or pressure not being released from an engaged caliper - depending on how the lining peels away. That is one reason why all rubber brake hoses should be replaced on older cars as a normal safety item. One long-time Mercedes mechanic said he found the O.E. hoses on benzes were good for 20, or so, years. Many have been left on much longer than that w/o trouble but should be replaced. Think about all that flexing going on over the years.