It isn't a big job to check, just lift the rear seat squab, the bottom piece, straight up.

The American built E53s didn't appear to have the heaters built in, so I don't know why the E70s would. Seems like a cost that the manufacturer could avoid, and they were pretty good at trimming things out of the E70 builds to cut costs (like tools, storage area props, etc)

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue