Well, first of all the shift motor, the reduction gears and the reduction gears bearings have probably never been taken apart for a good cleaning and repacked with fresh synthetic grease. The shift switches probably need to be taken apart for cleaning and fresh grease too. Finally, all of the electrical connector plugs on the bike need to be separated, cleaned with electrical contacts cleaner or other suitable solvent spray and refitted using generous amounts of dielectric grease in each one of them. If you do all those things well you'll fix it for good. You'll need a copy of the service manual to use for reference and some basic tools. You'll need a tub of NLGI#2 synthetic grease and a tube of dielectric grease. A tube of silicone gasket maker is recommended as well, for sealing up the shift motor during reassembly.
You can get a free copy of the factory service manual linked from this thread:
If you'd like some assistance pulling all of this routine maintenance off yourself, we'd be more than happy to help ya! Keep us posted on your progress. And welcome to the forums!