You need to go to LSC and buy trackers on the cars. After that the car will break. However, meanwhile another brand new copy is added to your garage. I spawned myself a Zentoro in this way. It's perfectly working.
I am wondering what some of the cars that can be spawned in are store-able for other people in their own garages. I tried it with the Go Go Monkey Blista and the Lost MC Slamvan and neither worked.
You need to go to LSC and buy trackers on the cars. After that the car will break. However, meanwhile another brand new copy is added to your garage. I spawned myself a Zentoro in this way. It's perfectly working.
A method to try is spawning in the car that you want to store in your garage, enter the hex code of the car into CE, take all the results, and edit them to the hex code of a car you can bring into LSC off of the streets. Then once you are in LSC, change the hex values back to the original hex of the car you spawned, then buy a tracker on it. I have not tested this yet, but I will later tonight.
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EDIT: if you also do try this out and it does work, please tell me.