buff,
Not tracking your van stock, is like not tracking your in hours parts stock - you are open to "shrinkage" - inventory lost & not paid for, certain techs have been know to do "side jobs" at your expense, van use, fuel, parts & labor (unless the van goes home with the tech & work might be done on weekends or after hours. Been do before, been done today, will be done in the future.
Also, periodic review of open work orders needs to be done - especially those where a lot of parts have been charged to but the work order is never closed. Another area where parts can be charged to but never paid for.

Just sharing some past experiences in the US, probably never happened north of the border - see the US has stolen Lord Stanley's Cup once again.
A life long Red Wings fan.