Bleed should be done every two years or 24,000 miles. I do mine yearly.
There is a special procedure for bleeding the brakes. The entire system needs done, not just the rear.
Should be the same as the Goldwing.
BRAKE BLEEDING SEQUENCE
1: Front Right Brake Upper Bleeder Valve
2: Front Left Brake Middle/lower Bleeder Valve
Rear Reservoir (under right side chrome engine cover)
1: Front Left Brake Upper Bleeder Valve
2: Front Right Brake Lower Bleeder Valve
3: Rear Brake Lower Bleeder Valve
4: Anti-Dive: bleeder valve on top
5: Rear Brake Upper Bleeder Valve