It just needs a clean out.
Remove the roller from the boomarang, if you have circlip pilers then pop off the clip and the bolt should pull through.
I dont have circlip pilers and tried to pop it off with a screwdriver (worked on other things) i snapped off a prong on the circlip instead.
You should be able to lift off the outer bearing shields (2 bearings) flush out the crap and repack with grease of choice.
As the bearings are not loadbearing like a wheel or pivot it wont matter if they are still a bit rough. You can push out the bearings if you remove the bolt, they are a standard size (unlike the E13 jocky bearings) or get a new roller, about £20 last time i looked.
Cup of tea, stanley knife to pop off the shields, clean out, dry out then repack. My inboard bearing seized, flushed with wd40 and worked it free by rocking back and forth, i wouldnt do that with a wheel or pivot bearing just replace them 😀