Hello all. We ordered the plate marker attachment from our 4800 table and when we got it installed it was constantly leaking air from the little white knob in the back. You could manually cycle the plate marker up and down and it would stop leaking for about 5 seconds then start again. I contacted Lincoln and they sent me a replacement plate marker that I installed and it worked fine no leaking. Then the next day the new unit is leaking air from the same place !!. Now a few things, the air pressure is regulated going into the plate marker unit (90psi), and what I'm calling leaking is its constantly exhausting air from that valve which i was told is a adjustable air muffler. does anyone else who has the plate marker, is this normal for the plate marker unit to constantly be leaking like this or did I receive another defective unit.