Oil looks good the first year but turns grey and then black as moulds eat it. Tried oil when I started out and then discovered what has been said already: cedar needs nothing.
A couple of years after oiling I took the the black mould off with washing soda and hot water and the hives now look silvery grey, which shows that I wasted money and time for no purpose.
One year I was pruning an old orchard in Kent and pulled a couple of supers out of the undergrowth. Judging by the age and the year the smallholding had gone to seed, the supers had been there twenty years and were probably EH Taylor or Lee's of Uxbridge, and made twenty years before they were abandoned.
Got them home, cleaned them, repaired a dent or two and they're as good as any I've got, all lovely and silver.