2016 Yamaha SRX 120 Service and Repair Manual
The 2016 SRX 120 closes out the run that Yamaha covered in LIT-12618-03-04, and it carries the code SRX120GL.
That one volume documents 2013 through 2016, so an owner of the last year gets the earlier specifications as well. Useful if a sled has been kept going with parts from an older machine, which happens often enough with youth models handed between families.
The procedures are Yamaha's own: engine service with torque sequences and wear limits, clutch and drive work, track tension and alignment, suspension and brake adjustment, and electrical diagnosis with the wiring diagram drawn in full. The maintenance schedule is stated as the factory specified it.
Confirm SRX120GL on the machine before you order, and use the code to pick the right column in the tables.