ChrisHager is right for the most part. For one there are a few videos on YouTube (use the keyword retrofit and that should help). Also, I had to do this for a retrofit and it was fairly difficult. I did it at about 275 for around 6 to 8 minutes, pulled them out and tried to pry them apart for a while, do the oven cycle again and repeat (the sealant cools rather quickly). I had to get the headlight so hot I had to wear gloves, and honestly, my sealant was so old it never actually softened, the heat cycles just made it brittle and it kind of gave up after a while haha nothing like you see on the YouTube videos where after its warm it stretches apart like a hot chocolate chip cookie. Good luck! Let me know if you need any extra tips or are running into any problems. Last tip: try to not pry on it once it cools, it will be easier to chip the plastic that way.
2000 Jeep Grand Cherokee Limited, Quadradrive, 4.7 V8
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