Chris & Randy,
Thanks very much for your help. I hate it when I break something without knowing what it does. I'm going to give the teflon tubing a shot - it's rated for -400F to +400F, compared to -100 to +175 for most low density polyethylenes. It remains flexible even with liquid N2 running through it, doesn't suffer from age embrittlement, and is chemically inert to just about everything. You can run 300F hydrochloric acid through it continuously with pretty much no effect. Do the other vacuum lines suffer from the same malady?