When you got the pulley kit from LET they included a new crank bolt. If it was a ASP kit I think everyone reused there factory one. Mercedes uses a torque amount I think 150 ft/lbs and then 90* turn. These are the settings usually done to achieve bolt stretch. It would probably be a good idea to replace the bolt but I don't know if you have too. It all depends on how much torque the factory bolt can take before stretch. When I built my vet I reused the stock crank bolt and there was never any problems