I have seen some coils for sale on web sites that the owners say the wooden exterior has been cleaned with boiled linseed oil. I thought I remember reading some where that was not a good idea, but can't remember why. Can someone remind me why that's a poor practice?
I don't clean mine with linseed oil but I do coat them after done with it.
I clean the wood coil cases with lacquer thinner on a rag. It has a tendency to leach the grease present on the wood boxes from 90 years of handling and clean them.
After rebuilding, I suggest folks coat the wood boxes (not top) with several coats of boiled linseed oil over a few weeks as Mark suggests. This has tendency to flatten out some of the warped wood sides that is commonly found.
If the coils fit the coilbox tightly and are hard to remove I suggest rubbing the three sides with a block of Paraffin which make them much easier to remove from the coilbox. Sometimes, I also lightly sand the boxes on the belt sander to take the high spots off, but go carefully, you do not want to change their fundamental shape/size.