Burfords as in Tricker's? In their burnished calf? What else do you use on these, Tricker's wax polish or cream?
I've taken to only using renovateur very occasionally as, in my very unscientific perceived experience, it seems to overly soften the leather over time if relied on too much.
@French_Touch, I use mink oil on my Bedales, Burfords and my Redwings, they were fine all last winter.
If needed, get them re-heeled/soled.