Hi, Cloud. I was only able to find some of the info you wanted, the rest may be in the manual and I just missed it, not sure. But here is a link to the service manual. Good luck.
http://www.kymco.it/contributi/download/MANUALI_OFFICINA/MO%20P50%20(inglese).zipAnd this is from the manual.
POWER DRIVE SYSTEM
TRANSMISSION CASE
Check the rear wheel transmission case
surrounding area for oil leaks.
Stop the engine and remove the oil check
bolt.
Place the motorcycle on its main stand
on level ground.
The gear oil level shall be at the oil check
bolt hole. If the oil level is low, add the
specified oil to the proper level.
Specified Gear Oil: SAE10W90#
Install and tighten the oil check bolt.
Torque: 1.0 1.5kg-m
Start the engine and check for oil leaks.