Provided its not actually got silver in it you should be okay, simple test though, measure resistance on your thermistor at room temp. Apply paste, measure again (make sure its not warmed up in your hand). Should be the same resistance with/without paste. If its not then the paste is electrically conductive, i..e. no good.
Simon Khoury
Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions