Axial play, how much is normal?

Some are better than others for this particular application, but any one will do. The important part is the way you do it: Not too much (1/8"- 3/16" bead max). Any excess will just squeeze out and go to waste. Let it set up overnight lightly snugged down finger tight before you finish tighten and re-fill. Mopar used to have a type of silicone they labelled "gear sealant" which is a grey or red/orange-colored variant that cures a little harder and is supposed to be more compatible with gear oils. But like I said, any one will do as long as it's applied properly. Permatex probably still sells the same stuff. Black would be my 2nd choice.