Contact Corrosion
WARNING: This page is about a different car, the 2018 Volkswagen Jetta, 2017 Volkswagen Jetta, and 2016 Volkswagen Jetta. However, it is still accessible from the selected car via links, so may be relevant.
Contact corrosion can occur if incorrect fasteners (bolts, nuts, washers, etc.) are used.
For this reason, only fasteners with a special surface coating are installed.
In addition, rubber or plastic parts and adhesives are made of non-conductive materials.
If there are doubts about whether the parts are suitable, then use new parts.