Currently having the same problem. I was using the Boywond, Annis ZR-380 and the modification was working for awhile, but after installing another add-on vehicle it stopped working and I've been changing the modkit IDs using the numbers provided and none of them seem to get the modifications and tuning to work. I don't know if I'm missing something or doing something wrong.
The original Modkit ID was 888 and the addon car I had installed was also from Boywond.
General Modding Discussion