Are there any Bitcoin block explorers still around that log First Seen by node data? Title..  Hoping to find out when a historical tx went into the mempool.  I'm aware this is transient data and not in the blockchain.  However i'm pretty sure I remember in the old days explorers used to log it.
edit:
i would like to find a block explorer that logs the first time its node saw particular transactions in the mempool, as opposed to the first time they were in a block.   ie:  I would like to look up a tx and see how long it sat in the mempool before it was mined.
Could you be a bit more specific?
There are a few block explorers that do provide information specific to their block explorer's running node.
Best lead I have for you is: https://bitcoinvisuals.com/
There's a lot of node information on there though I'm not sure its exactly what you're looking for.
However, I know that the owner of the site is pretty responsive and very easy to get into contact with.