I've got this unit, never had experience with tapes but always was charmed with the technology.

It was sold as "the state is unknown", and turning it the first time it appeared bricked - the "tape" and "clean" leds are both steady on, no activity at all and no reaction to eject button.

Inspecting it from all sides to find the locking elements/screws I've heard some rattling inside, and upon further manipulations I've managed to shake out this piece. It looks like some clamp that supposed to be pushed onto some thin rod/shaft, and hold something else from moving along the same axis.

It could have short out something, so I just powered the unit again. This time I've heard the head drum had spun up, the leds appear to blink as expected. The drive did take the tape, and ejected it also ok after pressing the eject button.

I've removed the covers from the drive. It looks the dropped clamp could not short the drive controller which is separated entirely from the tape bay area. But I just couldn't see the spot where this clamp could belong within the mechanism. It's like it does not belong it at all.
I found the web page (https://micha.freeshell.org/dds4/index.html) with the article on repairing the same drive type for the stuck head drum issue, and looking through all the pics I can't find anything remotely similar to this springy cap.

So what is it? Could it be a part of some cassette cartridge? But I have some HP tapes, and it doesn't look like that clamp has anything to do with it. Or was it just the bad storage conditions, and some garbage just got shoved into the drive?