This;
https://www.kbs-coatings.com/DiamondFinish-Clear.html is an excellent product, it may be considered a bit pricey though. I use their thinner to spray the bulk packaged product. It is also available in a spray;
https://www.kbs-coatings.com/Diamond...r-Aerosol.html
I have coated several under-hood parts on one of my vehicles, it has survived the harsh conditions without issue. I also used it for the clear coat, over the base color on one of my bike builds.