Mine failed from water intrusion. The gasket failed. Bulb carrier was rusted beyond repair. The LED board was good, but the connector was destroyed.

I have seen a lot of E70's with a wet right-inner tail light.

I found a new complete replacement assembly for ~$140. Shop around online.

Replaced the right inner light assembly and new gasket for left inner. It is an easy job, they snap in and out. Just depress the tab to release, you are not supposed to unscrew the nut as some directions on YouTube would have you believe.

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Current
2015 BMW F800 GT, Montego Blue
2012 BMW X5 Premium, Vermillion Red
2008 BMW 535xiT, M-Technik body kit, Monaco Blue
2004 BMW 525i Premium, Olive Green.

Past
1991 BMW 750iL, Alpine White.