Mansfield frost proof sillcock leaks at packing nut
My Mansfield frost proof sillcock leaks around threads of the packing nut and at stem only when backpressure is applied by leaving charged garden hose attached. I've replaced packing and packing nut O ring twice with no joy.
I realize leaving a charged hose attached is not a particularly good practice, but I used this sillcock with a hose timer all last summer with no leaks at all and just don't understand the current problem. Anyone have a guess at cause of leak and suggestion for repair? Thx in advance!