Nothing. on a '75 vintage if you want to do it the professional way, you remove the spanner nut that is almost the diameter of the lower unit, accessible from the rear with the prop off. Tales a very large spanner wrench that you can make from a piece of 1/4" sheet steel as I did. Lots of corrosion, meaning lots of superior quality penetrating oil, wire brushing the threads where it will unscrew, and a bear to get off. Then clean up everything real good and get hold of the splines in the bearing carrier (the alum casting part that is immediately around the prop shaft) it and jerk it out.... a slam hammer like body panel folks at collision repair shops and Harbor Freight carries for a few bucks helps.
Otherwise drill tiny holes in the outer seal until you can fish it out and then the one just behind it, being careful to not scratch/score the prop shaft. There are 2 seals back to back to seal against movement in both directions.....water in and oil out. May have the seals for sale on here or maybe ebay. Surely at a Merc dealer.
