They are probably just outgassing due to age and also less safety standards back then. They should be safe to use once cleaned. Be mindful though that some of the older (tube era) chemicals can degrade (and already would have) in a way that becomes corrosive and conductive (although this is rare, it's devistating as I have experienced this). So if you ever open something that's all inexplicably rusty inside only and has electrically leaky cloth wire insulation (might affect rubber too), that is why (be careful, I've heard this particular chemical is toxic, I think from arsenic). Although if it's not causing this and is entirely enclosed where the stink can't escape, I usually just leave it. But you should definatelty remove it from anything that has vents and especially fans.
Also, if you want to confirm if it's spray or something else, there should be a label printed somewhere inside the case (might be tiny or faded) that says something like "NOTICE: This equipment has been treated with (X) for (Y)..." and then a bunch of stuff about how not to disturb the coating.