Don't worry to much about the gasket, the oil return hole is inside it not on it.
If you still can't post pics, just tell us about it.
When you look at the inner part of the tach gearbox, does it have what looks like a bushing that fits into the large hole in the head?
If so, does the large hole have a slot cut through it at the bottom of the hole?
If yes to both these questions, can you see a hole under the bush?
The hole should/will line up with the slot.
Sam.
