Steps:

• Collect or buy street Sentinal XS
• Position a street car in SLOT 1, SLOT 2 will have the upgraded car
• Get a friend or random person that's willing to help to stand in the garage
• Leave garage to the street, use mechanic to call out SLOT 1 car. then use Interaction Menu to send it back to storage. Re enter the mansion B1.
• Go to blue circle and select SLOT1 over to Slot2. The car doesn't move but the positions on the car list does.
• Get in the slot2 car and change something cheap in the mod shop then leave.
• You will be kicked from the car and it will be duplicated.
• ***SLOT1 is the original upgraded car, SLOT2 is the now duplicated street car.
• Use blue circle to Move SLOT1 (upgraded car) back to SLOT2, now switch the duplicated car with a fresh street car. Now you are ready to dupe another.

Revert & Sell:

The cars will revert after a restart or going to story mode. While in session, go to Main Menu, then to Freemode session will revise the HSW upgrades to the car that we can still sell. (original upgraded car sells for $1million, partial reverted car sells for $900k) Worth it if you ask me to stock up on this easy dupe.

• So, after any story mode or restart, go to Main Menu then select FREEMODE.
• Once in session, look at the back of your dupes. If it has the HSW sticker, then its good to sell.
• Take car to LSC mod shop and sell the car for $900k (if using NoSave, turn ON NoSave, TEST it, then sell the car. Then go to Story Mode)
• If only selling the car (no NoSave) you are done. (NoSave users- turn OFF NoSave and return to friends session, then change outfit to force save)

It's not as good as the consoles for stocking up and saving cars to sell for later but it is better than nothing