[Al (astral highway)]

Hi Mike, and welcome to the forum!

I've encountered these transistors in a series pass application in a power supply from the early 80's. The chassis and cases of four transistors were remarkably rusty, but all four were still electronically intact, even though the hardware had rusted through in places.

A bit of fine wire wool will sort the rust if you're going to be running them hot and don't want to use a solvent.

Def don't cut open as Beryllium is indeed perilously hazardous and you will have a control of substances hazardous to health (CoSHH) sitch on your hands in short order!

These aren't high frequency types at all, so simply steer clear of applications where they need to be as there are far more suitable high frequency high power types.