You have to remove the compressor to remove and replace the seals, so you have to use the rope trick or the compressor trick (I prefer the former for the reasons stated above) to hold the valve with the spring and retainer and keepers removed to get at the seal, or it will drop into the cylinder. The air trick has the disadvantage of if you bump the valve stem, say while driving on the new seal, you kill the air seal on the cylinder, and down goes the valve, and the head has to come off. You don't heed 6' of rope - about 3'is enough, but more won't hurt...