As far as i am aware his second generation seal is the only one he has sold. A generation up from the Teflon seal fitted as standard. But my experience is that his seal is not as good. Many have reported it failing in cold weather. I have only ever fitted one and it failed after about three weeks. Whilst you have the compressor down it makes sense to replace the exhaust valve O ring. Secure it in it's seat with a very small amount of silicone sealant. Make sure the reed sits flush on it. And set the backing reed about 2 mm from the exhaust reed at the toe. The inlet reed should dead flat and sit flush on the head, no air gap between head and reed. If you hold it up to a lamp you can check this. Backing reed should be set with a slight gap at toe to allow inlet reed to move freely under suction, but not over flex. If you change the piston seal take out the piston and crank. Get hold of the lip of the seal with a good pair of pliers. Try pulling the seal out from between piston and retainer. If this works then get a sharp flat screwdriver and gently go round the retaining ring and lever it off the piston. If not just cut as much of the seal out as you can then use the screwdriver. Gently clean any burrs from the piston made by the retainer being pushed on. Very gently mind you don't want the retainer to be a sloppy fit. Put new seal on piston and press retaining ring back on to clamp it. It needs to be clamped firmly all the way round. I like to put four equally spaced pop marks just inside the joint of piston and retainer as insurance. To fit cylinder over piston present it at a slight angle push it over seal then twist square. One important thing when undoing allen screw that clamps crank to shaft make sure you use a good correct sized allen key, fully engaged using steady pressure. Usually 1/8". Using a 3 mm allen key will more than likely render the allen screw un-removable.
