B33 1947 oil leak question

[chaz]

not worked on a B33 motor before so bowing down to the knowledgable. Im working on a WW2 M20 with a later 1947 motor.
Ive been asked to change the oil lines , tank to motor and get running and starting better.
Ive removed the pipes a couple of times but cant get rid of the ol leak down on the crankcase, Ive changed washers , spotface is good, now, Im thinking the oil leak is from behind the timing chest. Ive managed to get it to start better so now the leak is more obvious as coming from the infeed area which makes difficult as its behind return line.
my question, going by Draganfly parts book the timing chest is cast  onto the right crankcase, which seal is likely to be leaking? the mag dyno seal or is there another culprit??  reasoning is, there is a oil film down the side of the case to chest almost looking as if its a two part construction.