1972 CR400 maintenance

helping a friend get his 72 Cr400 back running
he bought it new but can't remember much about anything on it
how do you change the gearbox oil, there are threads here to rebuild it
looking for the drain plug and where do you fill it?
is the screw near the kicker used for the fill level?
will have other questions
anything a known problem on these?
is there a service manual online or available? owners manual?

Source for manuals: http://www.3medesign.com/technical-data.html

Screw with the word 'NIVA' (level in Swedish) above it on the clutch cover near the kickstarter is the oil fill level - 1600cc (54 oz.).

Drain plug is under the gearbox on the bottom flat. The large plug on the angle towards the crankcase is to locate the shifting drum - Do Not remove.

The fill is the alloy nut on the rear top of the clutch cover with the vent tube nipple on it.

A bit heavier than the earlier 'round case', the 'big-clutch' engines are strong and reliable.