Hi Riff Raff
Good that you have a few spare SSL 4 pole double throw switches as spares but be patient as these may be frustrating to replace as Anthony mentioned as they were rubber sleeved decades ago and would be hard to access. SSL used H30 or H50 (3 or 5mm) Hellermann sleeves for this but you could replace them with heatshrink these days.
Another point: Sometimes and over time, various things can be dropped into the patchbay by mistake and there could be some loose screws or other metal parts which may be in there and I have seen a few over the years including XLR connectors lying around and loose.
If you need to access the switch, it is at the front of the patch and you may need to remove the Producers Table (horizontal grey material) to get access. If so, you may need to take out some of the patchbays (mostly user option rows) as well to gain access to the switches, circuit breakers etc.
If time allows, it could be a good time to remove any loose metal bits in there and vacuum clear the top side of the DL connector panel, especially as your console is so old. Also, maybe unscrew and put back the DL M3 screws as there would be a chemical reaction with the steel screws and the aluminium panel. If you remove the DL's and put them back, pull them down to notice the white cable labels on the wires as most of them will refer to the patchbay jacks (ie R16 is row R and jack number 16). If you do this, document the labeling as it may not be the same as your installation manual pinouts, assuming you are lucky enough to have a manual and it is accurate, which is rarely the case these days!
Here is a link to Farnell for the 4 pole switch which looked the same as SSL used but maybe a different supplier these days.
https://uk.farnell.com/multicomp/1m41t1b5m1qe/switch-4pdt-5a-120vac/dp/1550192Good luck and if you have time, do what I mentioned above at the same time as it will save problems later on.