Vivitar 650 PZ camera external shutter opening very slow?

Have a Vivatar 650 PZ Data Back AF Series 1 camera w/ 38-110mm Power Zoom Lense. Upon powering up zoom advance, external shutter leaves will either not open or open very slowly. I have blown out stutter slots with compressed air and have lubed area w/lite oil to no avail. Can you recommend a repair procedure or adjustment to restore shutter action. Thanx.