**I don't know where folks are coming up with the requirement for staining cedar shingles.
The advantage of cedar shingles is that they DO NOT NEED any maintenance.
They naturally weather to a pleasant gray hue, and ..... FOR NO MAINTENANCE SHOULD BE LEFT THAT WAY**
They built a few new homes around here in the late 60's using cedar shakes, with no preservative. Within 10 years, they looked pretty nasty, between being weathered down a way from the eaves, then still looking brighter up under the eaves. They also got like a black mold on them, and not black streaks from nails, just a nasty looking black on them. All of them have now been resided with vinyl to cover it up. Could be it had something to do with us being in the rust belt, 100, or so miles upwind from the coal fired electric generating plants, and the acid rain they produced.
I have no idea what "kind" of oil was in the stain, but definitely not creosote, the smell of creosote would have given that away. But I'd imagine it did have some Linseed oil in it, plus other types of oils. I do remember it pretty much being very thin, and the first coat really soaked in. I remember Dad getting it in 5 gallon pails, and using a paint paddle on an electric drill, to mix up the pigment that was settled in the bottom of the bucket, before filling a more manageable gallon can to work out of.
We've never had the first problem with Carpenter Bee's, or Woodpecker's attacking the siding. Although the Carpenter Bee's do seem to love the exposed Yellow Pine, and Fir framing lumber. Close to a dozen Carpenter Bee traps hung around the covered patio, and outbuildings seemed to have thinned the herd quite a bit. A good way to use up scrap lumber from the wood shop.
There's actually 2 layers of shakes on. 1 smooth underlayment, then the textured shingles applied with, like 1-1/2" galvanized, ring shank nails, because that is what they used back in the day. No rust, and still on tight. Sheathing is 3/4" Yellow Pine, nailed on at a 45º angle, so as not to have an open crack, at a nail row. Then a layer of felt paper to make it air tight.
It's been working well since before I was born, and I'm getting to the age, it may need one more coat in my lifetime. As long as I don't have to do the serious prep work like the last time, it will be a piece of cake.