1979 Mercruiser Alpha 1 Gen 1 - Installed new water pump and everything looks good but, cannot get bottom half to slide back into place. It stops about 3/4" of an inch from going back together. Spline shaft is well greased, just acts like it comes up against a hard stop and I don't want to force it. I've tried the usual things like rotating the shaft, checking the 'O" ring in the upper splined receiver and checking water pump connection. I have not had this problem when working on other similar outdrives. One more thing, it came apart fairly hard. Any ideas???