1972 suzuki 125 tc

I had a TS-125 back in the day, which is a similar machine, and I believe I used 20W50 in the gearcase. Use a motorcycle-specific oil to protect the wet clutch. Probably holds about a quart. Can't remember if there was a dipstick or an oil level plug to check the oil level. Sorry, that was 37 years ago.
Mike
'71 AJS Stormer 370
'73 AJS Stormer 410
'02 Honda XR400R