just keep track of the mileage. take pictures too. take a picture of your ex cluster as you take it out of the car. and of the si one when you put it in the car make sure the mileage is readable. that way if you do ever decide to sell it you can give actual mileage of the car. in the future all you would have to do is.. ex cluster mileage + (new si cluster mileage - old si cluster mileage) = true mileage.