Richard:
Have you tried pumping the capacitors down and then
pouring in the oil? Probably from a jug which is also connected
to the capacitor and evacuated first. That is the general
procedure for vacuum impregnating transformers, and seems to
work well. Not sure about the water aspirator, though, because
there will be water vapor in the system.
Ed Phillips
[ This is the technique that I used and my cap is still working after 15kV
-- Chip ]