Taranis- Polyolefins are a type of plastic glue nerds call a "low surface energy" plastic. Kitchen cutting boards are another an example of a low surface energy plastic.
Low Surface Energy plastics tend to have a very complete molecular structure (translated: they're very smooth) with not a whole lot of dangling ends. Since they don't have an abundance of dangling ends, adhesives don't have much surface roughness to wet out against.
There are a few things you can do to low surface energy plastics to make them rougher, but that's not the lesson here.
We have some new polyolefin bonders, but they're going to be too rigid for use in this application, so that kills the thoughts of using a two part adhesive of some sort.
I've been using that heat shrink lined with hot melt from Fastenal for years now and would come closer to using something like that before I'd consider using a polyolefin bonder. When shrunk, this stuff is moderately stiff, so confirm for yourself if you think it'll be too stiff for use before putting it on a brake line.
No, really, the mustache means I love you.