Is there any way to open them up and clean them out? I dunno what it is, but they're ugly lol.
With very little coercion, mine separated out just fine. There was a sticky type of sealant I had to deal with but really didn't seem to be glued into place. Maybe it was the age and it had deteriorated I don't know. Maybe someone else has better info.
If you heat it or anything?
Yes, you mildly heat the seam with a heat gun and *gently* separate them. The adhesive that bonds the inner and outer together gets much softer with heat.
You can throw them in an oven to soften the glue more evenly
I would recommend getting new butyl tape to put them back together, that way if they ever have to come apart again it'll be possible
I bought some for my headlights but at the time I was doing my tails I didn't have it and just used clear rtv
They look awesome and are completely sealed but I doubt they would come apart without breaking