I doubt that is an issue, Mark. The foam is just there to protect the electrostatic element, and looks to be sonically transparent (at least on my older Lambda Pros). Also, a few years ago the foam on my Lambda Pros partially disintegrated (after about two decades), and I didn't notice any sonic difference as that occurred.
Eventually I replaced the pads and the foam together, with a replacement kit purchased from Audio Cubes II. In case it becomes relevant in the future, I believe (although I'm not totally certain) that the replacement pads they offer for your newly acquired SR-404 come with replacements for the foam as well, and both are installed simultaneously.
Best regards,
-- Al
Eventually I replaced the pads and the foam together, with a replacement kit purchased from Audio Cubes II. In case it becomes relevant in the future, I believe (although I'm not totally certain) that the replacement pads they offer for your newly acquired SR-404 come with replacements for the foam as well, and both are installed simultaneously.
Best regards,
-- Al