I came upon this 'SuperLube Synthetic Grease' http://www.guncity.com/superlube-syn...-85-gr.-117304
We're giving it a bash. Certainly the pumping effort has been reduced markedly so we will see how it performs over the long term.
The debate about mineral oils (fuel), high pressure/temperature, oxygen/air ratios would seem to be deserving of a thread on its own?