Biggest difference on the E53 was the LCI (commonly referred to as the facelift) that happened for 2004 models. Lots of changes that year. 2000-2003 years were pretty similar, as were 2004-2006 models.

Small items like the glue used on the headlights are part of any manufacturer's continuous product evolution program. Another way of saying it is that you shouldn't believe much that you read on eBay.

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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