However thin the coat of oil is, it will migrate down to the wood when stored muzzle up. Leaving the metal unprotected and the wood with oil doing it's best to soften it over time. The only thing that stops the oil migration are horizontal surfaces like for example the action face when stored muzzle up.
One of the problems is that the people who designed everything from the guns themselves to the products used to clean and protect to the design of safe interiors.....none of them expected guns to last 100-150 years. So never imagined problems appear for vintage guns. My vintage guns typically arrive in quite a bit less than pristine condition. They have been used, abused and ignored for decades at a time. Currently just about everything I have is pre WWII and most are pre 1925. The oldsters are from 1885 through 1900.
With the except of renewed CCH, addressed currently in another thread, the object of my restorations and care is to give them the best chance at another 100 years of effective service. So that means researching and applying best practices of care once the restoration has occurred. And it means no shortcuts in the restoration process. I can think of no better source of best practices than actual London and Birmingham gunmakers who have spent 40-50 years making and restoring fine London and English guns. So that's whose advice I seek and trust. And when I am discussing work with a Canadian smith I am judging his proposed approach against what I have learned from my discussions with gunmakers in London and Birmingham. We all know that in NA, there almost is no better recommendation for a SxS smith than that he is of English background and learned his trade in London or Birmingham. Whether it is David Trevallian or Nick Makinson, those men arrived on our shores competent in both understanding and skill.