Check the Valve Stopper, there was a problem with the TM G26 series and they made an aftermarket one to replace it (it forms hairline cracks that unless you take it out to look you will never see.
If you cant find a replacement one on WGC or UNc, search for it under the P226 they are the same part as per Arnies. Although I'm not sure if KSC version is the same as the TM ones...
*edit - Illusion has 2 in stock on his parts page.
