Deleted the vehicles.meta under:
\A_Sports\dlc.rpf\common\data\levels\gta5\

Added a new file:
<?xml version="1.0" encoding="UTF-8"?>
<!-- A DLC Pack by gurufix -->
<CVehicleModelInfo__InitDataList>
<residentTxd>vehshare</residentTxd>
<residentAnims />
<InitDatas>
</InitDatas>
<txdRelationships>
</txdRelationships>
</CVehicleModelInfo__InitDataList>

Didn't delete its code this time... starting game again and checking. . .

I don't know if this behaviour could possibly be Windows fucking around with my files and doing some kind of file recovery each time I restart my PC.