The one field (to my knowledge) where there is recorded long-time experience with what drying oils do is the field of oil painting, some five hundred years worth.
Both the artsy portrait painters and James Virgil Howe agree that the best film is made from cold-pressed (not steam distilled) linseed oil. This may be purchased in 2 oz thru maybe pint bottles at a good art supply store, or on the internet e.g. wwwdickblick.com,
www.cheapjoes.com.
So-called "boiled linseed oil" at the hardware is steam-distilled oil with driers added - to dry faster. The film strength is not so good as with cold pressed oil. But it drys fast.
Oil does thicken with heat, which is good for a stock finish & for that I offer for your consideration that you get some "stand oil", from whatever art supply suits you. The price of these two types of linseed oil is no more than that of modern stock finishes.
About real turpentine, which is most likely to be found in art supply sources, the art guys say: "Pure gum spirits of turpentine contain hydroxides that react with acids in drying oils to bind free oxygen", which means it helps the oil film "dry".
Besides art history, we have our own history at least in US military muskets. They were finished with hot, real, linseed oil. Lots of these are still around with finish in good shape after two centuries. I have a couple such in my den.
I think the downside of such finishes is that they can hide the grain, at least in walnut. Some manner of resin-varnish-modern finish may be better in this respect. My 19th century John Shuler half-stock rifles were finished, apparently, with some manner of dark varnish. Early 19th century Lancaster powder horns had the base plugs varnished, with red pigment added.
Plastic? A personal matter. Me, I like to use old stuff on my old style weapons.