Preventive Maintenance

Is there anyone who can helpo me in understanding how to set up preventive maintenance in this scenario:

Customer performs on a specific truck preventive maintenace at 500 hours usage, using a model wok order that calls for some spare parts (filters etc), while when he reaches 1000 hours usage he needs to call for a completely different set of spare parts.

To accomplish this I set up another model work order on the same schedule with a different set of spare parts for the 1000 hours maintenance; nonetheless the system when running R12807, at the 1000 hours reading, generates the first maintenace wo  for the 500 and the second maintenance wo fo the 1000. The requirement would be to generate the second model wo only at