Oops!, I thought you were talking about the axle breather hose.
While its apart I would replace the flex hose. Take a close look at the steel lines too, they can rust through and corrode, not to mention that after 30+ years the inverted flare nuts can rust to the point of welding itself to the line so when you go to unscrew it, it just twists the steel line.

 

Exactly! I was able to loosen my right front brake flex hoses from the flare nuts. But the left front was sacrilege: I had to put vice grips on the flare nut and turn while keeping the flex hose 5/8 nut from moving. Only way to do it. The flare wrench I had was rounded the edges of the flare nut and finally rendered it useless. Even after soaking the damn thing in a gallon of PB Blaster!

The rear wheel cylinders I got lucky on and got the flare nuts loose, with PB blaster treatment. The flex line on the rear, to get the right and left connections loose, you have to pull the hose away from the axle slightly to get a wrench around them. We shall see 'bout those two! Then the other buggar is the one up near the top of the left shock absorber where the flex hose goes back into the steel flare nut coming from frame. I'm making a prediction that I'll be using the vice grips on that one. And even after that, I bet I will end up twisting the steel line.

And doesn't help that the truck had a leak in the bed on the left side, right above where the flex hose goes to the solid brake line. Caused more rust issue than it should have. And I don't even live in Yankeeville Rustaway Salt-on-da-Roads...

 

Do like Earthquake said and replace ALL flex and hard lines. Doesn't take that long or cost that much and you should never have to worry about mashing the pedal and going "OH S**T".

 

Happened to me once on my 66 mustang back in 1979. That car had a SINGLE compartment MC. One hose broke and the whole system *****!! Had to use the emergency brake to stop.

 

got all the fittings off. The flexible hose fitting up near the left rear shock tower finally came and didn't twist the metal line. But you're right, probably need to think about replacing.