Now while I'll agree on an early change, I could note find anything other than 4K for schedualed changes in either the owners manual or the service manual.
However having thirty years of hydraulic systems experence I can tell you that while the base oil may not break down in 4K miles it buy no means indicates the oil is still servicable.
Take note our common motor oil starts with a base oil ( petrolum or synthetic, which does NOT have any lubrication quality past a french fry)
to this base additives are added to reduce wear. These additives vary but are extreamly fine less than 1 micron in size. What happens to these additives over the course of time is what makes the differance.
As your oil gets dirty, either airborne or from internal wear, the additives tend to cling to the dirt or metalic particle until the particle grows large enough to get traped in the filter. This action reduces the lubricity of your oil and is why old oil will trash your ride. Now we need to understand the quility of our oil filters to help us chart our oil expectancies. A standard automotive oil filter is rated at about 90 micron, your better filters are rated at about 45 microns, twice as good! the smaller the number the better. In my world of hydraulics 10 micron would trash my controls and possible cause a machine run away with mind blowing catostropic results.
When new oil is put into my hydraulic tanks it HAS to be pumped thru the filter system because, brand new from the factory, it is still to dirty for my systems. We filter to 3 to 5 microns at the valve.
Have you seen the adds about cleaner base oil? I can't remember the brand, but that's what there getting at, starting cleaner.
Now lets get back to our beloved Runes. Changing the oil more frequntly will only assure us that we have clean, properly functioning oil to make all those little parts stay smooth and shiny. You will note that the manual warns aginst ant oil with graphite or molybdenum, because it would make our clutch slip. As for castor based oil, if I could find Franciscan Racing Oli I would fill'er up, light'er up and close the door and get hi, I love the smell, all the flattrackers around here used that in the OLD days.
So change that oil, change that filter and remember storage time does equate to miles as moisture helps create acid in stored oil.
Jack