first check its not running down from the back of the rocker tin. the back corners leak if...
1) you do not do the nuts up tight enough
2) you have done them up too tight and warped the cover or compressed the rubberized cork seal into a thin piece of varnish or tree bark
when you do the nuts up you want to take up about 1/4 of the height of the seal on its first compression.
clean up with brake cleaner
check again.
if still unable to ascertain
take off lower inspection cover below converter or clutch
if there oil is on the back of the block and flywheel its probably rear main
in which case check out your PCV set up and make sure it works before doing anything else
most will leak a bit if the PCV is blocked or not connected
OR on a v8 you have PCV and vented cap on the same bank of the engine
oil doesn't tend to migrate up
but it will go everywhere coming down even if it gets out of a gap a long way up.
it will migrate down and back dependning on speed of car and how much air you fan moves
if its a rope seal it will ooze a small amount all the time because you can't get asbestos rope anymore. which actually worked.
when a rear main goes properly...! you leave a puddle behind, everywhere you go.... unless you are doing this id be inclined to drive on, my friend.
while you are under there see if the sump bolts need another quick nip up... motor has now been heat cycled and gaskets take a "set"
and did you use a decent copper washer on the oil drain plug? that is 1 leak that gets whipped around the bottom of the bell housing by the air flow
Dave
