I " seasoned" every barrel of every ML' er I have ever owned.
I do not ever use any petroleum distillate solvents in my ML' er.
I have never had any problems with plastic fouling or " powder rings" in my bore.
And while " crude oil" may be an acceptable lube and seasoning agent Hoppes, Break-Free and the rest are refined petroleum products and are not necessary for the cleaning, seasoning and lubing of ML' ers.

To season: Remove the bbl from you rifle. Boil some water in a tea kettle. Holding the bbl w/ a towel, pour the water thru the bbl unti lit is hot. Take your swab totally saturated with bore butter and swab the bbl back and forth for several minutes or until the bbl begins to cool slightly. Let it sit to cool completely. Use dry patches to remove any excess. Done.
I also do this periodically after cleaning or target shooting.
It works great for me.[:-]