No, almost all rare transistor types on eBay are fakes.
The TLDR here is that some parts are no longer available and that’s a certainty. If unavailable parts suddenly appear on eBay, usually somewhere in mainland China, walk away, unless you like throwing money away.
There are lots of parts that I wish were still available, but they’re not and we move on. Sure, an old guy in Poland may appear every so often with a box of special unavailable parts, but you can usually pick these legitimate listings by looking for a variety of markers and other clues. Everything else, like classic Hitachi 2SJ56 and 2SK176, VFETs, rare STK modules etc listed on eBay are fakes. I don’t mean that these parts are probably fakes, I’m saying with 100% certainty that they are definitely fakes.
How do I know? I’ve been at this a long time now, I’ve had excellent mentors and a ton of my own experience to back it up. I have a couple of specialist semiconductor vendors, one in Japan that is especially good and if they can’t obtain the parts I need, nobody can. I’ve also examined and tested many fake parts over the years.
Unscrupulous sellers know that inexperienced buyers are willing to do almost anything to get hold of mythical, unobtainable parts. So, they take existing cheap parts and have them printed with whatever the unavailable part name is. The end-user tinkerer buys a few and installs them and they fail, or the problem remains.
People buying these parts on eBay are not technicians. How will they know, let alone prove the new part is fake? How can they be sure there is not some other reason it failed? Will they even know if the new part or the equipment is performing correctly? You’ll see the rabbit hole here, and it’s just not worth going down.
If you took your equipment to an expert, they could test it for you and let you know if parts are genuine or fake, and what the problem actually is. This is why I generally avoid fitting customer-supplied parts. If the parts are not sourced from large commercial vendors or other specialist parts suppliers, you can’t trust them. There are perhaps one or two good parts sellers on eBay, but that’s it.
In many cases, you don’t actually need these rare or unobtainable parts. I have stock of and access to many rare NOS parts, parts that are generally unavailable to the average shopper. Then there are modern replacement parts that work perfectly in most cases and I have an extensive database of good substitutions and can engineer a solution where I need to.
Don’t fuel the fake parts industry or pay crazy prices for fake parts.