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Hello, it is normal that you have some rattles when you engage the 1st gear, even with the clutch totally free. In fact, gearbox axles are running a short time after you press on the clutch by inertial movement. If you wait a moment, axles are stopped and it become very difficult to engage the 1st gear ... On my 57, I try to engage very smoothly the 2nd gear, just to have a smooth rattle, and when the rattles are stopping, I engage frankly the 1st gear. No problem with this manner !
On the 57, the clutch is dry, don't put oil in it ... just grease from time to time the clutch lever.
For the engine, a good 20W50 oil is perfect, I use Castrol GTX or Shell but all reputed Marques are OK.
Good luck