Leaking input shaft

I have recently modded my craftsman to go 22mph. However, it is leaking oil at a good pace from the input shaft. I decided to fill it with 10w 30 oil i had because it came stock with grease. I put 1 quart in and it leaks from the input shaft now. It is a spicer/dana and i know, i heard there crap.
So could it be a bad seal or is it too full?  I really appreciate any answers.

I don't know much about what transmissions have what, but some you can replace the stock O-ring to a seal. You might also try something thicker like just filling it with STP oil treatment, or you could try 80w-90 gear oil. Might make it leak a bit slower at least.

Oh, and WELCOME to ATLTF.COM, don't forget to post a bunch of pictures of your machine

if it's leaking from the input shaft, it's likely both too full, and a bad input seal... is it leaking from the axle shafts? oil doesn't need to be fuller than the bottom of the axles.... it will ride the gears up where it needs to be