@rodkinal if you can provide the sample of raw data that you have we can create a query that would work for all combination. Above one is just run anywhere example based on data you have provided.
Based on the details provided if you already have field names as car.nissan , car.bmw with corresponding stats, all you need is to plug in the final stats command to your current search returning the fields i.e.
<YourBaseSearch>
| stats count(car.*) as *
If this does not work then maybe the data/extracted field is not of the form you have mentioned (multivalued fields need to be handled differently then single valued field etc). So, for us to assist you would need to provide some mock sample data as you are getting in your raw logs.
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