In the picture below I have shown a repair to the instrument panel back-up supply line on my '06 12X but to the right of that is a splice with four brown wires. The single wire heading back to the rear of the bike is the rear R/H blinker. That splice is covered with glue-filled heat-shrink and can hold the wires in place with an internal electrical break.
When I repaired this I moved the join about 1 inch closer to the instruments and the join in the wire going to the rear a couple of inches past the loom-guide to get any joins away from the loom-guide area.
That repair has held up for 46,000km so seems to be a reasonable approach.
Of course this may not be your specific fault but now you know where this splice is you can do some more focussed fault-finding.
The three wires heading up towards the instruments go to the blinker switch, the instrument panel and the front R/H blinker.
The symptom you have indicates a fault with either the rear R/H blinker power from this splice back to the rear blinker or the rear R/H blinker ground wire. Given the ground goes to one of the earth points under the seat my money would be on the power wire at that splice.