Sorry for the late reply here, it must be frustrating not getting any responses!
Anyway, myself and a few others have had the same problem as yourself. Has the bike seen any kind of moisture recently? Water ingress can cause this problem in the lights (the factory 'seals' on the lights are, ahem, crap), though to be honest just general vibration can do it too.
I had to replace most of the individual LEDs on both sides, and I also needed to get the left hand circuit board/wiring fixed by an electrical guy, as something had shorted out - he fixed this easily for just £20. LEDs were a couple of quid/dollars. Brand new tail lights from MV are about £300 for the pair, I believe, so it's must more cost efficient doing it this way!
Replacing LEDs is pretty easy, and just requires that you have a soldering iron to resolder each individual LED onto the mount. Pulling apart the lights is just a case of undoing the various screws that hold each section together. The most difficult part (not really that difficult) is prizing apart the lights using a combination of heat (heat gun/hairdryer works fine) and a thin knife. It all seems daunting, but it's actually really easy. Just take your time and be methodical. I have basic motorycle DIY skills and I managed it.
I put the lights back together with some heavy duty waterproof black silicone adhesive (being careful not to let it smear onto the lights) and it is now impermeable (in theory!). be sure to use alcohol or meths to thoroughly clean the lights inside and out.
Here's a link to the original thread where this problem was discussed
DIY Rivale/Stradale tail light fix. There's a video on there discussing how to do the LEDs, but to be honest it's not that much help. You'll figure out the process yourself, I am sure!
Cheers,
Nick
