Ive clocked up over 3000 miles on my Raven Sport Tour since I got it in January. I do about 50 miles a day couriering in London. I heard that the gear oils needs to be changed at that amount of mileage or 12 months. Is that correct? How do I know it needs it? Are there tell tale signs like noisy gears etc? Is it a straight forward job like changing oil on a car, or is reassembly required? I am not good with such matters if thats the case. Does anyone know any bike shops in London that could do it?