Every MacOS update, I do run a sudo command and get the password prompt. I cancel, and instead do...

    sudo cp ~/Dropbox/etc-pam.d-sudo /etc/pam.d/sudo

Type the password once and you're done. I've been carrying this around for quite a while. No need to edit the file every MacOS, just copy it.

But once it did utterly go south when Dropbox's "load files on demand" functionality replaced the file with a bunch of zero bytes. That wasn't fun to fix. So maybe Dropbox isn't the best storage place.