Butyl is a glue that is often used in car restorations to seal and reseal areas of the car such as headlights.
Previously, butyl-ropes were meant for "universal" applications, and true headlight butyl only came in blocks that was nearly impossible to apply. However, thanks to Morimoto's Retro-Rubber, there is a headlight specific product rather than having to re-purpose a product that was originally designed to reseal windshields and sunroofs. This product is perfect for your retrofit!
Why do we need butyl? Butyl is designed to function as a sealant, so its' main purpose is to seal.. Duh! Butyl creates a seal around the headlight and prevents moisture from entering and creating condensation in the headlight.
How do you apply butyl? Heat! It is recommended by many retofitters to heat the substance and light using a convection oven. However, it is possible to use heat the sealant using a heat gun, but it often doesn't create a even heat and ultimately seal.
In conclusion, butyl is a relatively inexpensive product that will make a drastic difference in the success and longevity of your retrofit project.
Looking to purchase butyl for your next "fit". We can help! Retrorubber is available for purchase here: https://sparksmith.com/products/retrorubber-headlight-sealing-glue?variant.