Mardy,
The only problem with oil leaks that I have had has been the oil cooler adaptor oring under the oil filter, when this leaks the oil can travel to the back of the motor very quick, the replacement oring is slightly thicker than the original, if you are having trouble with the rubber seals for the crank and distributor shafts, make sure there is plenty of lube on the sealing/wearing surface when it is installed as it can wear the new seal very quickly.
Brian