These are often never inspected until there is a brake problem, however, we should be checking them at least once a year – particularly if you have the original single circuit master cylinder and drum brakes.
As a matter of interest, I checked two hoses that I replaced some time ago because of a problem I had with one wheel cylinder not releasing once foot was off pedal. I replaced the cylinder but still had the same problem.
The hose on that wheel looked in very good condition, however, the other side hose which wasn’t giving any problems looked very old and rusty and had a large split in it. I cut both of them in half and the rusty hose with the cut (superficial at this stage) was still working fine and not leaking and I could blow through it with my mouth. The nice new looking hose on the side I was having problems with was almost completely blocked with GUNK and there was no way I could blow through it. Obviously, under pressure when applying the brakes, fluid was forced through, but when brake pedal was released and fluid no longer under pressure for its return, it was not able to flow through blocked hose – hence not allowing wheel cylinder cups to retract.
The moral of the story is not to judge the condition of a hose by its appearance. If in doubt, remove it and you should be able to blow through it with ease. If not, then throw it away and replace it. Don’t forget the rear rubber hose that goes to the brass junction on the diff housing.