I purchased a used Robinair 15102-A vac pump last winter (much better
price off season). Now I am ready to use it. I added oil (did not
replace the old oil since I was doing a test evacuation) and hooked
the vac pump up to the vehicle's A/C system. I was able to pull 26 or
27 in of Hg of vacum. As I understand it I will need to pull 29 in of
Hg to properly evacuate the A/C system (after repair).

Will changing the oil have an effect on the pump's performance (pull a
stronger vacuum)? I searched for a manual or an exploded view of the
pump with no success. What other sort of maintanence might I need to
do to the pump? Other than hooking the pump up and letting it run,
are there any other proceedures that I should / need to follow?
Suggestions / links to info very much appreciated.