I totally agree with Lord Voltermore. If our dealer would send me an e-mail with such an offer for the next service, I will e-mail back:
"If that oil flush is or could be of any use, why don't I find it in the Honda service schedule at all? Not after 5,000 miles, not after 50,000 miles, not after 150,000 miles. Not even after 1, 2, 5, 10 or even 15 years. Can you explain that to me?"