It's simply this: any asset seized must go to the general fund, not into a law enforcement fund.
If a local police department seizes cash or a car, that asset goes to the state. If federal law enforcement does the same, it goes to the treasury, not the FBI or ATF or the Justice Department.
This small change would remove the incentive to seize assets for any reason other than stopping criminals.
We also need due-process reforms, but this would be a good start. Government departments should never profit from criminal activity.