I have a pre-alpha outdrive that had an alpha 1 lower unit. I replaced the yoke end seal because I was getting gear oil in the bellows. I then changed the lower unit to a pre-alpha because the lower unit had a big crack in it. The lower unit I am using now has the pre load pin which shouldn't matter because the upper unit is a pre-alpha. when I try to put the upper and lower unit together they stick about 1/2 inch apart. I have tried without the water tube and made sure the shifting mechanisms are lined up. Finally I tried the old unit and am having the same problem. Is it possible for the gear in the upper unit to slide down. When I measure the length of the shaft it seems longer than the space I have. Any thoughts?? Thanks!!!