Best TIM for Xigmatek HDT-S983

I was wondering what people think would be the best TIM for a Xigmatek HDT-S983 would be I have read that some TIM'S don't work very well with an exposed copper base and it was recommended that you don't use a material based on silicone oxide as it will cause oxidation to the copper heatpipes upon contact. I am not sure what TIM it was that came with this heatsink (just came in a little satchel with no name on it) but I am sure I can do better. Any ideas? Just looking to improve temps a bit more.

I use AC5 or MX1

Tim Consultants TC-0098 Thermal Paste .. (And here we go again )

Would be nice to try the Tim Consultants TC-0098 Thermal Paste but i cant find it in Australia at all. Does anyone know of a place to buy this here in Aus.