i use old engine oil in mine, cos ive got plenty of it, it only gets flung off anyway. doesnt seem to do it any harm.
I was lead to understand that while you can use old engine oil on cheap roller chains - thats what I used on the old GN250 - O rings and X rings really don't like all the microscopic bits of engine in old oil, apparently it buggers up the O rings. 
well yes and no. certainly, in a lab with the right amount of measuiring equipment to hand you might be able to shopw that old engine oil isnt as good as new engine oil. but lets face it, i bet the bearings shells cams and pistons in my engine give the oil more grief than the chain does, and they have the same oil in there for thousands of revolutions per minute. where on the chain its dribbled on and then works its way off again. im sure if it contained anything that damaged metal and rubber, it would have damaged the engine bits first. besides, thats nothing to the grit and dirt and debris that will become encrusted onto the chain in use, i bet they do it more harm than the oil.
