[QUOTE=230/8] The soft fat rubber hose was/is used at the ends of the plastic line where connections are made to a fitting and/or sharp bends are needed which could crack the plastic tubing."

Thanks 230/8. That answers my question. Over the years my SL not only had the soft fat rubber at the ends of the lines - but sometimes slapped in the middle of a hard plastic section.

I see the previous point about the diameter change probably not making a difference, but all the repairs to my vacuum lines over the years had the effect of adding many more places for leaks/loose connections - not a good idea.