Just doing a small repair to a friends MX5 exhaust. When replacing the oxygen sensor I would think it would be a good idea to put some kind of antiseize compound on the threads. However I do not want to risk contaminating the sensor since they are rather costly to replace. Will a smear of copper grease be OK? or is it necessary to use a specific product? or nothing at all! Any ideas and advice would be most welcome.
Regards Geoff Peace.
G’day Geoff
Copper slip won’t survive the exhaust manifold temps. Mine had nothing on it when it was removed about 8 months ago, just undid with the proper sized spanner. 
Agree with Geoff, I have tried both copper slip and moly grease - both burn off but what they leave behind can help a little. I have used both without any problems…
New o2 sensors I have fitted in the past from MX5 Parts already come with what looks like moly grease on, but this maybe just to enable smooth replacement on corroded threads.
Rich