I have a 1988 Ford F-350 with a 7.3 idi motor. leaks tranny fluid

What is your question?

I was plowing yesterday morning and I went to the gas station to get diesel I get in to leave and put it in gear and no motion what so ever just a little crawl .. I added some aft and was able to drive about 5-6 miles and leaked out again I stopped and looked under and it's just pouring out of the drain on the bell housing what seal would that be????? Please help