No! Don’t do it, almost all rare types that appear on eBay are fakes.
Certain parts are no longer available and that’s a certainty. If unavailable parts suddenly appear on eBay, usually from Shenzen, China, just forget about them.
Trust me, there are lots of parts that I wish were still available, but they aren’t and we move on. Sure, an old guy in Poland may appear every so often with a box of special unavailable parts, but you’ll be able to detect these legitimate listings.
Everything else, like classic Hitachi 2SJ56 and 2SK176, VFETs, rare STK modules etc listed on eBay are fakes. I don’t mean they are probably fakes, I mean they 100% definitely are.
Because mystical parts like these are no longer available, unscrupulous sellers know that inexperienced buyers are willing to do almost anything to get hold of them. So they take existing low-spec parts and have them printed with whatever the unavailable part name is. You buy a few, install them, and they fail. How will you prove the new part is fake, versus there being some other reason it failed..? Do you have the technical ability to do that? Will you even know the new part failed..?
If you took your gear to the right place, a specialist could at least test it for you and let you know if it’s a fake. But beyond that, this is why I generally avoid fitting customer supplied parts. If you aren’t buying parts from the large commercial vendors that the manufacturers use and other specialist parts suppliers, as I do, you can’t trust the parts.
In many cases, you don’t need these parts anyway. For example, I have access to parts vendors that sell NOS parts and I keep many NOS parts in stock. There are modern replacements in most cases too, so don’t pay for fake parts.