Oil Leak, bad- please help

I have an '88 mkiii non turbo. I started leaking oil from underneath timing belt cover from a small machined hole. I consulted a friend that said it was probably the main seal. I replaced the seal, and it still leaks oil from the same spot. There is no oil leak when the car is on, only after it has been run for longer than a few seconds. It's a considerable leak, for a short period then stops.