If WD40 gets into any wood it will swell, in this case making the hole smaller.While this was probably a jokeit's actually not a bad idea to put something on the end of the string.
I think my personal solution to this would be Light, slow, careful reaming - just a few strokes - along with some sort of lube on the end of that string - either a graphite type lube, or maybe even a coupla squirts of WD40.
Other than concern over making the hole too big for strings with no silk wrap, I’d be inclined to open the hole a little.
