Maybe the spline is not quite engaging as you put the leg up into the engine half. Perhaps a little wiggling of the prop to get the splines engaged as you push up?
I have tried this, didn't seem to helpIt definitely seems to be a metal on metal sound though so it must be something getting stuck somewhere.
Well, there must be a locating peg somewhere.
I had a Volvo Penta MBA2 which was basically BF75 engine, I never had much issue wiggling the leg back on.