The dealer is not obligated to provide you with the lowered rate. If you made a deal without specifying that they lower it should the rates change they will definitely not just lower it for you.
2008 335I 6MT, ZSP, ZPP, ZCW, CA, 6FL, HD. Retired
2006 330i 6MT, ZSP, ZPP, ZCW, CA Retired. 2004 330i 6MT, ZHP, ZCW Retired