ive been trying to put this rear tranny seal in for 2 days now and to no avail i cant get it in . it wont go around the input end of the driveshaft and its way to big and wont lock in the spline area. i got the dust boot off. and now i have abosolutly no idea whats wrong now. i think that i have the wrong rear tranny seal. can anyone confirm this

its a federal mogal
part number 1990
and how far in does that seal go .. i hit it and it wouldnt seal .. man i need some help!!