The problem with my cluster was with the motor which drives the RPM needle. So what I did was split the two clusters and use the rear section of my original one and the front section of the new one with all the motors so the original mileage was intact.
As far as I know the mileage is stored in two places in the E36, the cluster and the ECU. You can reset the mileage manually but it will only sync the two places to the highest number out of the two.