The marcel iron was much smoother after the second cleaning. I did rinse the iron quite a bit, and I had to heat the iron to get excess water out of it. It seems to have some tiny holes near the handles that I think water got into.
The approach I used worked well enough. I can also ship the iron back to Golden Supreme for them to clean it as well for under $20 + shipping.
To each his own - I may try this procedure again down the road if the plates begin feeling rough again. I did not re-temper the iron. I may do so. It works fine as is, but it may work even better if I re-temper the iron. I have a separate article on this blog about tempering.