ΔE 23.6, loose: different enough that you should pick on purpose. Brown Wash is noticeably lighter, much more saturated than Nuln Oil.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Brown Wash is noticeably lighter, much more saturated than Nuln Oil.
The same difference applies the other way round: Nuln Oil is noticeably darker, much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Nuln Oil on the colour wheel See Brown Wash on the colour wheel
All matches: Nuln Oil equivalents · Brown Wash equivalents