petec

There are few choices here.

If it is an early block they used a rope type rear main seal that had locating pins in the rear main cap and the slot in the block. If these were not removed and the rear main seal replaced with a rubber type you will get a leak.

It could also be that the rear main seal halves were put in level with the block and main cap which can also leak a few drops when the oil gets hot. I usually offset the seal a little so one end of each half is goes down into the opposing surface.

I will rule out the oil pan as in my experience the pan gasket leak would trickle down the outside of the block plate.

xswoopr

I have a master cylinder leak and it looks just like what you described. It runs down the line onto the bellhousing and drips off of the spacer plate.

fastbackford351

Just tell anybody who asks that it isn't leaking. It's just marking its territory.

JamesW

It's a Ford... it will leak.

Love your Mustang..it's marking it's territory....

my77stang

+1

also, seals wear into the crank, so when you replace them it could be riding in the groove and still leak from that point. a "seal saver" could be installed and would make the surface nice and smooth again. i'll take a pic of my 289 crank to show ya what im talking about

GypsyR

Dunno about experts, but I'll offer what I would look at.
1. The rear intake "cork" seal. Famous for seeping almost undetectably out the rear and forming nasty black drops right under the rear main seal are.
2. Even though you refuse to believe it, still the rear intake "cork" seal. Seriously.
3. Bumped slightly up the list because it is aluminum. the oil pan.
4. Valve cover gasket (s) leaking only ath the rear, fooling you into thinking it's the intake or rear main seal.
5. The rear main seal again. Why has been pretty well covered already. Another reason (for folks using "one piece" main seals) is some newer seals shops use are... well, crappy. The new thing out there is a "teflon" rear main seal. Not available for all engines though. They cost 2-3 times as much as regular replacement seals, but as far as I can tell they are GREAT and will last as long as the engine.
6. The flexplate bolts. Some Ford cranks are "through drilled", some not. The ones that have flywheel/flexplate bolt holes all the way through need some sealer on the bolt threads or oil splash in the pan can wick down the threads and end up on the flexplate. Generally these leaks will spread oil all over the flexplate. This is a "slow" leak and generally doesn't produce so many actual drips.
7. Weird stuff. There are oil plugs in the back of the block that rebuilders remove and replace. They are pipe-threaded though so about the only time they leak is ifsomeone completely forgot to tighten themand theyhave fallen out. This causes an Exxon Valdez sized oil leak pretty quickly.
I once found the Dorman plug (like a freeze plug) that covers the camshaft bore to be leaking. Apparently installed incorrectly during a rebuild itstayed mysteriouslyleak free for almost two years then started leaking for no apparent reason other than to just really really annoy the hell out of me once I finally discovered what it was that was leaking. Surely sucha problemis very very rare though.
8. Weirder stuff. Like the brake fluid drip mentioned above. That wasa new one on me. Always something new to learn.