So it is still there, you are just missing the DLC again. You need to re-install the Exclusive Content For Returning Players unless you have it unlocked naturally and it should show back up in your garage. If not, it is blacklisted or was removed by Rockstar if you glitched it in using my tutorial. I haven't had time to mess around too much since the patch to see what is still working in terms of vehicles. Pretty sure this happened last patch too @Chvrche5