I noticed that the fill probe was letting air by. It looked as though one of the O-rings was scuffed. I went through an O-ring kit that one of our technicians had, but they were all too thick and, with them fitted, the probe wouldn't enter the gun. Anyway, long story short... Does anyone know of the actual dimensions of the O-rings on the fill probe? ID, thickness should do it. I've seen a kit of six on the web for £ 4.50 that are for the HW 100 fill probe, but I'm sure that, given the right dimensions, I can get them from RS for pennies each. I apologise in advance if this has been asked before.