Here's the real stuff. Genuine olde fashioned marine Stockholm tar. Accept no substitutes.
http://www.tarsmell.com/tar.htmlIn my years around traditional wooden boats, I often encountered folks who tried to use roofing tar, horsehoof tar, road tar, yadayada... I've never encountered anything that works--and looks--like the real deal. Opinionated? Nah.
There are a lot of boatbuilders who have secret formulas for "boat sauce" or "boat soup." Many of them are just adding a dolup of tar to some other marine finish. About as easy and traditional as you can get, though, is equal parts by volume of true Stockholm tar, genuine turpentine (I've heard some claim "mineral spirits" is as good, but I don't think so), and boiled linseed oil. My only secret ingredient is a small shot of Japan drier. You can make it more expensive, but you can't make it better, IMHO. You might want to fiddle the proportions some to increase the turps, but keep the tar/BLO about equal.
Apply, let it soak in, apply again, etc. Big hint: it kicks off with exposure to UV. Those who have trouble with the stickies use too much at a go and don't set it in direct sunlight to cure. Using other tar products eventually results in a dull black finish that's hard to do anything with but keep on oiling and claim it's traditional.
Use the real stuff, use the sun, take your time. And show us your results!