I have changed my oil several times and as far as I know you must remove the fork. When i change my oil I drain the shock upside down for several minutes and then flush it out with a little new oil. This is just the way I do it. Also one other note - i went from a 5 wt oil to a 10 wt oil in an attempt to stiffen the shock. Beware, the change from 5 to 10 was HUGE. The shock was so stiff, it took me all day to re-adjust the clickers. You can get Bel-ray fork oil at Bobs Cycle for only $8 qt, not much more than Mobil 1 oil. If it was me I would stick with fork oil and use only one brand for consistent results.