I have a dead side marker light now (amber) and rather than hassle with a warranty replacement, plan to just order it direct from command electronics - about 8 bucks I think. Remove the lens and look at base - there should be a part number.
Whatever you do, seal it well when replacing bulb or lens. Really a bad place for water intrusion and attention needs to be paid to keeping them water tight.
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Smooth Sailing,
Ric and Jan Golding
Southern Illinois
2016 Jayco Seneca 37FS
2016 Chevrolet Traverse
2018 Cheverolet Silverado