Bike is 1959 Dommi 99. In case this is relevant to the problem it has a commando clutch.
When starting off from the house first gear is engaged with no problem. However, when out on a ride and stopping at traffic lights I have a probem. Neutral is easily found. But, when it's time to move off I struggle to engage first gear. It requires a combination of gentle letting the clutch in to turn over the cogs and shuffleing the bike to and fro with my feet. I fear this means something in the heart of the gearbox is worn and needs replacing ! During the rebuild I replaced bearings, bushes and seals in the gearbox using an RGM supplied kit. Possibly I've missed something else that should have been replaced ?
I am using Castrol EP 90 oil in the gearbox.
Mike