A warm welcome to the realms of Vincent ownership. The gearbox is lubricated with two pints of oil. This will bring it to the lower level of the flat on the gearbox.
The primary drive is lubricate with enough oil to bring the level up to the level plug on the primary drive cover. Even this can be reduced leaving just enough for the run under the clutch sprocket to dip into.
Hello, I have always used engine oil in both primary case and gear box, in my case SAE40 oil.
The gearbox level should be kept just on the bottom of the flat of on the dip stick, if you have a Standard clutch as this helps prevent the oil working through to the clutch. John.
Some people might remember that a gearbox dipstick is I believe, part of a spoke and is screwed into the handle. Therefor it may have been disturbed at some time and the flat portion may not give the correct reading of two uk pints showing on the bottom of the flat. My solution is to rub the flat area with a wet and dry production paper, paint it with a matt black paint so that the shiny oil shows up against it. Put 1 3/4 pints in, check the level and keep adding small recorded amounts until the oil shows on the flat. Literature says this should be done on the rear stand. Sidecar blokes should take special care as I reckon that the level would be well over two pints to record on the dip stick flat and if that is the case, I suggest lenghtening the stick to suit.