So I finally got all the O rings I needed for the job. I took my time and it went well with just one snag. I couldn't get one of the heater hose fittings off the old tensioner. I hit it with liquid wrench, tapped it with a hammer, but it wouldn't budge. The other one twisted off, but lower one, no go. I ended up undoing the pinch clamp on the hose, and worked it loose and off. I then removed the tensioner. I put it in a vice and carefully hack sawed a slim section of the tensioner around the fitting. That enabled me to spread it a bit, and I was able to twist it out with a pair of vice grips. The O rings were flat, and I could barely tell they were there. I picked them out with an awl, and cleaned the fittings. Popped the new O rings on, brushed some grease on them, and they slid in and sealed. I used new GM O rings on the Dorman aluminum elbow, and they sealed as well. No leaks. I am a happy camper.