I have heard the you MUST use spline grease when installing the out drive back onto the boat. (Also on the prop shaft) What is SPLINE GREASE and how is it different? What happens if I use regular grease? I've no problem with using spline grease. I'll go buy some. Just curious what I am getting for my money.

It is some real sticky green grease. Thats about all I know.

its designed to protect and lubricate the spines

I prefer to use merc 101
but merc spline grease works great also