Think worst Risk Case. Start preparing for a trailer, or lodging, or something else but donít drive it. Just is not worth the chance of wrecking it. Your dreams may go up in smoke Ďcause it is a tough call to put the kind of bucks into to fix the shredded motor or just part it out. Ask any SEL owner about timing chain rails.
I have the same car, same paint, same concern, well still have vacuum but the oils seems to leak out after a few hours of sitting and I get a similar noise as you. I donít know for sure that it is the pump, but because I canít pinpoint to within 3 inches to were the sound is coming from (like I can a lifter), I have to go with the worst risk case scenario. After much ado Iíve just rented a car until I can get the pump in this weekend.
But if the belt tensioning spring or shock is going it will make a very similar knocking or tapping noise. Take your broom stick, etc and push down on the plastic pivot piece where the spring and then where the shock attaches and if it is stops knocking that may be your noise source. Then on to your brakes, which would be something else but do check out the belt tension spring and shock condition.