Hi, hope someone can help, I'm currently working on my bike, and would like to know the correct grade of gearbox oil to use in it. The original manual says 900Ml of 10W / 30. Could someone advise what would be the right equivalent oil. Many thanks, Andy

Take a look at www.bobistheoilguy.com/viscosity-charts. Notice that the low number winter viscosity oils [ 5W, and 10W]  correspond closely to 75 wt gear lube and the SAE 30 engine oils correspond to an 85 wt gear oil. 75W-90 gear oil is about as close as you will get to 10W-30 engine oil. Why not use use 10W-30 as Montesa recommended.

Many thanks for that advice. I will stick with what they recommend. Im not sure if you can help me or anyone else on the forum as I'm rebuilding a Amal carburettor for the bike. I've had the carburettor sonically cleaned and have purchased like for like replacement service parts. My question is on the jet pilots. There is a original 0.40 and a 0.20 in the original float chamber that I have purchased like for like. From the photograph could someone confirm they are in the right place. Many thanks again, Andy. 0.40 at about 9 o'clock, 0.20 at 6 o'clock

Their placement is correct. Size 40 jet at 9 o'clock and 20 at 6 o'clock.

That's great news, thanks, I know I don't know you but the advice today on Christmas Day is very appreciative. Hope you have a wonderful festive period, keep safe, Andy