Yes, the problem was the oil in the wood, PR doesn't shrink as much as some people think, what you most cases see in a separation, is the wood shrinking away why...?? because the wood was not totally moisture free when cast with the PR. PR as it cures, produces a fair amount of heat, if the wood has any moisture on it, it will some immediate shrinkage that, can increase as time passes by, why..??? because if wood is not totally dry and moisture free, it tends to shrink as it dries and reaches equilibrium to its environment.
This is not a rule set in cement, there are always exception to any rule and in this case, it has a lot to do with the type of wood, wood shrinkage will the same regardless if cast in PR or Polyurethane (Alumilite).
Now, specifically to your problem, if you are considering to cast some more of that wood, make sure you put it in an oven at 80° celsius for about 6 to 8 hours, have everything ready so that you get the casts done before the wood gets cold but, do not pours the resin immediately after the wood comes out of the oven, the ideal time is when you hold the wood and you just feel some warmth.
Oily wood needs to get its oils crystalised by "roasting" the wood, oil gets neutralized that way and therefore, offers a much better adhesion surfaces.
You should "always" use very thin CA in the joint of the wood and resin after the blank is clean, that will guarantee a better adhesion and, if there is any small gap in between the 2 materials, the thin CA will soak through it and seal the deal. You can CA the resin piece that to its place and re-finish...!
Good luck,
Cheers
George
