It was my understanding from a `Foreign Policy’ political science class during that time period that the US specifically withheld vital spare parts and used their supply as leverage to make sure the country buying the armaments listened carefully to our suggestions and advice.
Of course that may have changed under Peanuts.
What they taught you was a half truth. The purchaser knows the U.S. would like to hold them hostage to U.S. policies, but they refuse to enter into such a contract unless they can secure at least enough logistical supplies to make it worthwhile to enter into such an arrangement with the U.S. The U.S. “sometimes” makes an effort to limit the ability of the customer to go it alone without the U.S. as a supplier for the fleet, but doing so has to be balanced to the minimums acceptable to the customer in the contract. The class was being misled about the extent to which such policies could realistically be implemented in a given case. When we were training the Iranian air force personnel, their training was or was not identical to our own training, depending upon the extent of the security required for that occupational field.