I think this guy has 5 of them. Probably is the one from this post:https://deskthority.net/keyboards-f2/help-identifying-for-a-newbie-t13375.html
Their condition probably doesn't vary much so the seller probably didn't bother to take extra pictures. They should clean up nicely though. Here's mine that I actually found locally in a basement of a bowling alley. Apparently they had some use for it in scoring bowling games or something in the late 80's.
The thick brown residue was no doubt tobacco tar that bowling alleys are known for. Interestingly enough, all keys sensed properly without needing to internally clean the capsense PCB.



