If you wanted to put all customers in 1 table The only way I think you could do it would be to create a customer database (for customer info only) and a "transaction" database that contains info about the transaction for the car and a "hierarchy" database.
The hierarchy database would be a related portal off of the transaction layout, on which you enter the other "customers" and their hierarchical order. So your entry into the portal for your example would be:
Dealership 1 name
Dealership 2 name
Leasing company name
Lessee company name
If you wanted to search for all cars related to a business you would do a search for the name in the hierarchy database and all of its related records in the Transaction database. It would find all final customers that had some dealings with that company.
Since you could have many customer records linked to many vehicles this is a classic many to many relationship.
Your fields would match like this:
Vehicles::VehicleID = Vehicle_Customer::VehicleID
Customer::CustomerID = Vehicle_Customer::CustomerID
You can place a portal to Vehicle_Customer on a Vehicle layout and use it to select existing customer records to link them to the vehicle record.
You can place a portal to Vehicle_Customer on a Customer layout and use it to select existing vehicles to link them to the customer record.
That said, you might want to separate your customer data in to Companies and Personnel as a way to link multiple people to the same company.