What are my options for x-drive transfer case fluids? Dealer says their bulk stock is low and won't sell me any, and ECS says it's on national backorder. So I can't get the BMW fluid. Alternatives? Other than letting the dealer do a drain and fill for $350.

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'04 E53, 4.4 Sport
'97 E39 528i
'86 911 Carrera, track car
'96 BMW R1100R