Leaks oil from where ?
Reconnect everything and measure crankcase vacuum through the oil filler.
If you don't have a gauge accurate enough, make one:
This is a water column pressure gauge, one end is open to atmosphere and the other to the crankcase (it has to be air tight). You then look at how far the water level at multiply by two to have the pressure in In of water column (InWC).
It should be 4 to 6 InWC of vacuum.
What engine do you have?
Threaded Mode
