Isolastic Grease?

What kind should I use?

Use silicone grease, or red rubber grease.

Being in the states, I would use Mil-comm's TW25B, MC1210, these are high grade greases. I have used it on seabourne weapon systems and would not hesitate using it on my Norton, it can be bought in the UK, contact me and I'll let you know of the dealers here that sell it.