I second Tom's comment. I cracked the end cover of my 365 back in the day and I took it to a motorcycle shop to weld it up. They did a super job and never gave any problems after that.
But have you convinced yourself that is where it's leaking? Presumably, you're already certain it isn't something stupid like the drain plug and it's not a missing seal or something like that. If you're unsure, you might try wrapping paper towel around where the seals are, where the end cover is bolted on, the underside of the case where the two halves join, output shaft seals. You can put some inexpensive thin oil in it to check.