Franky, thanks for sharing the photo shots, glad the corrosion caused by the leaked caps didn't do heavy damages there, and look like all traces still intact except for that half pad, btw great cleaning job you've done there.
Btw, this confirmed that these particular hv transparent film cap is cursed, in this thread alone already two proven cases, hope this will help others in the future as reference and replace them before bad thing happened.
I guess you have many home works to do for this beast, btw just remember, when powering the whole scope without the enclosure, make sure you have a big fan blowing the "whole" giant A1 board with the scope up side down position, so those unobtainium hybrid ICs get cooled properly.
Looking at your fan's date code, year 2004 ?
Wow, if its the original fan came with the scope from the Japan factory, then your 2465B is definitely quite fresh imo.
Regarding your missing caps at A5 board, suggesting after you desoldered the old Dallas chip, install a good dip or sip socket for the new Dallas DS1225 chip, so it will be easy to backup & restore the calibration in the future.
Btw, spotted another missing cap at your A5 board at the right upper corner, besides the screw pointed by the red arrow. Also there are other A5 examples at this post ->
Here for comparison.