[Healeys] massive oil leak

[healeymanjim]

changed oil in a club member's tri carb.   went to get gas and noticed lots of oil under car.  by the time i got back had lost about 4 qts or more of oil on a few mile drive.  coming from rear of engine and coming out bottom joint and cotter pin hole. was only a small drip before oil change.  assume it is coming from rear main, but could it fail that fast?   any other places to look?