I've used the tester tint spray before. it works but doesn't hold up. after about 8months and 2 weeks of over 100degree heat, it cracked and peeled off.

i just wiped it down again and resprayed.

but this time i sprayed the inside of the housing instead of the outside. it takes a long time because you have to spray a little then let it dry, then repeat but holds up much better then spraying the outside.

this was on a 96 gti vr6