Everyone has things they swear by, and sealants for engines seems to be one of them. Back in my Norton days I gave up on Hylomar because I found it would only remain leak free for a few thousand miles. One of my buddies mentioned that his Yamaha dealer used some stuff called Yamabond to keep the oil in his two stroke dirt bike, and I figured if it could keep that motor dry it was worth a try for the Nortons. It was, and it worked very well. When I started working on Airhead BMWs it was only natural to continue using Yamabond (now a days called Three Bond 1209), and it continued to work well. Right up until the day I pulled a cylinder for a compression bump upgrade and found ThreeBond almost blocking the oil passages leading up to the valve gear. Clearly I'd used way too much of a good thing and almost caused me a bunch of trouble in the process. So when the Gurus on the Airheads mailing list recommended Hylomar because if too much was used the extra would float harmlessly away in the oil, it made sense and I started using it again. Of course my old tube from the 1980's was dry, but since those days Permatex started carrying it and a quick trip down to Kragen's and I was back in business. However, it seems Permatex is no longer distributing Hylomar, and while my tube should last me another ten years, there are other Gurus that contend, as I had found with the Nortons, that the Hylomar would not provide a good cylinder base seal over the long run. And these guys recommend the Permatex equivalent of ThreeBond 1209, a silicon based sealant.
One of these Gurus is Ted Porter, principal of The Beemer Shop in Scotts Valley, California. I visited Ted one misty January afternoon to drop off a transmission for a mainshaft circlip installation, and during the course of our conversation I mentioned the Airheads sealant thread. He offered to show me how he uses the silicon based sealants.