ITC rules

A taxable person purchased an oil tanker paying GST Rs 7 Lakhs. In the year of purchase he takes ITC Rs 7 Lakh on the ground that he will use it for both taxable and non taxable supply. In the first and second year he used the tanker on RCM basis .He did not utilized ITC.
In the third year he sold the tanker with GST liability of Rs.4 Lakh and utilized the ITC and rest is reversed without any interest because there was no net cash liability.

Now my Query is that whether there is any violation of GST rules in above transactions
and
RCM facility availed by him was legal as he has taken ITC
Please advise.