Can't find info about addon card for HP-150 #VintageHPComputers

Sonno Ocea

I dismantled my HP-150 to check if there was anything wrong and while I was at it I tried to take some decent quality pictures of some of the board.
(the crt driver, backplane, and psu required a total disassemble so I didn't take picture of these)
Link to Google Drive folder.

One things that really bugs me is the board that I labeled as "MISTERY-PCB", I have no clue on what it is, can someone please take a look and direct me to some documentation?

Also, all the light blue capacitor (22uF 25V) on the VIDEO and SERIAL PCBs are leaking a green substance and I want to swap them for MLCC equivalent so they last way more.
My question in this case is: should I do that? Or should I go for another electrolytic cap that will leak again but is less out of place?

Last question is: the 8MHz AMD 8088 can get quite toasty, should I stick one of those small heatsinks (for raspberries) on top of it?

Any help is welcome, have a good evening!

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