I got a comment from Mr. Martin, that Google changed their SMTPd, so I'll have to revisit the article.
As suggested, new /etc/postfix/smtp_reply_filter would be:
#New 2016/09:
/^5(\d\d )5(.*. \S+ - gsmtp.*)/ 4${1}4$2
Above one is working perfectly on my box.
Again, thanks for Mr. Martin for bringing this topic to my attention.
