Hi... I just came across your post researching the same issue.
The MFG number on my roller tube is 918EH20.001U & SKU Number is 9108976202. I called Dometic and was given the same replacement part you were. B3313161NR.020 The "NR" is the Onyx color awning. Was quoted a price of $533.07 plus tax and shipping. Have you replaced yours yet? What was the correct fit? THANKS Bob
So far yes There's been a few minor problems but nothing serious. There's no MH that's doesn't have some issue or two the owner has to deal with ( and some of is self induced).One thing we did was upgrade the mattress the original set up was the bed from hell.