Is there any reason not to use a chemical duty diaphragm pump on a vac oven? Ones commonly used for rotovaps? I have one on my oven currently and it pulls down to ~40 torr or -28.5" Hg on the gauge.
Figure that would be more forgiving if the cold trap gets warm.
How often do you find you can run it before needing a rebuild? I thought they were pretty tolerant to most solvents? Maybe less so to terps?