Here is a list I have compiled of Mod Shop labels for use in editing carcols files.
Using these for tuning parts will allow parts to correctly show in Los Santos Customs, not just the trainers. I will continue to add to it as more are found, tested, and verified.

Full list has been done, however I will now take all entries and categorize them for easier reading. I will also include carcol sections for base use when adding tuning parts to make them easier for all of you.

Special thank you to @Unknown Modder for complete list!