Any Ideas?

["Alexander Christoforou" <Alexander.C@domain.elided>]

Hi All,
    I have a question regarding the Vacuum retard unit on the distributor. I
think that the diaphragm is bust. To test it, I took the other end of the
hose coming out from it and tried to suck on to it and then plugged it. I
removed the cap and looked for movement, and also waited to see if the unit
held vacuum. Would this seem to be a good test on the device?
    Could you also suggest hoe much of a difference this unit makes on the
running of the engine, cos I am lost to its purpose.
    One last problem. I seem to be having oil dripping from the rear end of
the underside of the car. It seems to be coming from the diff, but am not
sure. I read somewhere that jacking the car in a particular way possibly
cracks the seals (?)

I appreciate any help with these problems.