a gear from drivetrain to odometer? lol, definitely not.
and the answer is no. The ECU does contain the mileage, but anyone who has enough skill to replace a cluster can also fake the mileage in the ECU.
People who reprogram mileage on cars can do it so well that the dealer cannot tell its been done (so you can return over-mileage lease cars without penalty)
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2002 TiAg M3 6mt
deoranged, dechromed, led tails, ZHP knob, UUC SS v3, GROM, OEM 220M 19's, Michelin Supersports
2006 YZF-R6, black, ohlins, pazzo, BMC, cat delete, vance hines csone, YEC racing tune,-1 +2