Hello Pete,
I'm sold on Mobil 1 Synthetic Grease. You can find the specs. at
http://www.mobil.com/USA-English/Lub...tic_Grease.asp
If you go to this you should remove all old grease, it's never a good idea to mix grease. Please don't ask me why, this is what our Aerospace Lubrication Engineers recommended.
There's a lot of solvents that will work to wash away the old Grease, but I use Simple Green. It takes a little longer than say Kerosene but it's a friendly Solvent, to you and the Environment.
Happy Camping