Are these something I should grease or oil? If so, which one? It seems like something that should be lubed but I know the first time I just grease something up it will turn out to be made of a special polymer that corrodes instantly when exposed to lithium... or something...
"It is never too late to be who you might have been." -George Eliot
Friction in the track is largely due to the sail slides rotating under load and binding. This can be the result of the slides being attached to the mainsail with webbing tightly sewn so that it does not allow the slides to rotate and align with the groove.
Of course you need to the correct slide and profile for your grove.
I am working on a new universal adaptable slide to eliminate this problem.
Lube your slides with a good dry lube by all means: clean the gunk off them first with some solvent: white spirits or the likes. And if you're brave, or better still: if you have able/willing crew, clean the track out with a rag. Then go ape with dry lubricant. There's a certain American product that keeps Sailing Anarchy's B.S. flowing freely- they claim it works on blocks and deckgear too, but there are also several other extremely good makes of dry lubes as well! It MUST be dry, because atmospheric pollution will stick to oils etc and render your clean track as sticky as a bad reputation.