Find all files in the /var/log directory that are not compressed (not ending with .gz) and execute the command 'sed -i -e 's/\([0-9]\{3\}\)[ -]\([0-9]\{3\}\)/\1-\2/g' {}' on each of them.
find /var/log -type f ! -name "*.gz" -exec sed -i -e 's/\([0-9]\{3\}\)[ -]\([0-9]\{3\}\)/\1-\2/g' {} \;