Hi The Silver Jubilee model was 1977, from memory I think Mollydog is correct, and under the gearbox there is a small bolt within a bolt for checking the g/box level, make sure the bike is level or on its centre stand. There is a
2nd bolt in the gearbox underside
DO NOT REMOVE as this is the hydraulic plunger that locates in the Gearbox quadrant that selects gears and removing this one by mistake can lead to 'gear loss', between the crankcase and outer case cover(left hand side) there are about 3 small holes that allow a small amount of oil through to keep the primary side lubricated. I am at work at present so dont have my old Bonnie manual to hand. If you get into any trouble don't hesitate to get back and post.
As said, this is stretching my memory back 29 years!
