Jerry told me about this technique at MOOTMAG11, and sent me the link. It is another version of the "film trick" posted earlier.
http://sealmate.net/
I made a similar tool from an empty plastic food container, and used it with good success on a leaking fork seal.
Well, guess what? It also works on seals for rotating shafts -- at least the one on my Brush Hog mower. There are two right angle gear drives on the machine. One of the input shafts was leaking badly -- so bad that when I filled the box with oil to the recommended level (until it just runs out of a hole in the side put there for this purpose), the oil immediately ran out of the seal. It is not clear to me what I have to do to replace it, but I suspect I must remove the box from the mower -- a major task, but doable if necessary. As I was disassembling the drive to this box, I remembered the seal cleaner trick, retrieved the homemade tool from the box of Magna parts, and used it on this shaft. It still seeps just a bit, but the leak rate is way down. I am hoping that after running it some, it will reseal completely as the seal expands where the grit had been.
Thank you, Jerry!!