The HPR, undo the two locking grub screws then two of the biggest Allen keys up each end and separate.
If it's been stubborn you can try heat cycling, boiling water then freezer. Make sure all threads are clean when you put it back together.
Check the comparison videos on youtube, some of the GoPro alternatives are really good.
The GoPro style mount is used on a lot of accessories.
If you get an underwater style sealed case they can take a hit but the audio suffers unless you mod and run an external mic.