In my travels I have heard of this one.
The leech is in fact an interesting little creature. It produces an enzyme/oil that is part of it's digestive system that increases blood flow and works as an anti-coagulant so that it is able to feed.
Now, my problem is that I have done some digging on this and this goes all the way back to the early 1990's which were the Gary Griffin days.
Where we ran in to problems was trying to figure out how physiologically rubbing this substance on the outside of a penis on the skin could have any effect.
If major research were done, it may be possible to create a cheap version that could work out of this that would induce an erection or work as an ED treatment. It would have to be biologically cleansed and either done transdermally or in injectable to be useful, but, as weird as it sounds there is some potential if researchers were to work in that direction.
One thing that may be on the net where we had no information in the early 1990's would be the medical usage of leeches as an erection treatment by some primitive tribe.
If that were found, and it it were proven out that the useage of leeches would induce an erection which would indicate both blood flow and localized anti-coagulant effects, then there could be something to it. We in our research years ago never did find this kind of informaiton. Not finding it did not mean that it did not exist, it simply meant that we did not find it.
I might suggest a few days of digging on this one.
The other thing about the leech oil is that last time I looked it was incredibly expensive and very difficult to find.