AIR CYLINDER LEAKS

I HAD PUT UP A POST BEFORE ABOUT THE REAR CYLINDERS ON A CIVIC ALL OF A SUDDEN NOT HOLDING AIR BUT I COULDNT FIND ANY LEAKS,SO I TOOK THE WHEEL OFF AND FOUND THAT WHEN I AIR UP THE CYLINDER THE AIR COMES RIGHT OUT THE PORT ON THE BOTTOM OF THE CYLINDER,IVE ALREADY ORDERED TWO NEW CYLINDERS FOR THE REAR BUT I WANTED TO KNOW WHY THE AIR CAME OUT,THE PORT IS OPEN,NO PLUG,BUT I CHECKED THE FRONT AND ITS THE SAME WITH THE PORT OPEN BUT IT DOESNT LEAK.IS IT THAT THE SEALS HAVE JUST GONE BAD?