I may get flamed here because I'm not an expert, but I have spent the last few days replacing all my vacuum connections (not the whole lines, just the connections) with silicone tubing. Go to the model airplane store and buy silicone fuel tubing. I've used it for years on various projects (including model airplanes) and have never had it rot, harden, stretch, crack, or loosen up. These are precisely the problems I found with the mercedes rubber. It's about .50 a foot, withstands very high temperatures and seals tremendously. You can put the hard line very close to the male connector and still make a 90 degree bend, no problem. I also used some vacuum grease on the exterior of the male parts to help seal things and allow me to remove the tubing if necessary. Otherwise it grips so tight you have to cut it off. This works for me.