GR translation: patient as shoe grease against the rain

[Mike Jing]

V471.33-36, P479.26-30    she looked at him once, of course he still
remembers, from down at the end of a lunchwagon counter, grill smoke
working onto the windows patient as shoe grease against the rain for the
plaid, hunched-up leaky handful inside,

What does the phrase "patient as shoe grease against the rain" modify here?
Is it "the windows", or is it "grill smoke"? The 2nd edition of the
published translation treated it as modifying the windows, which doesn't
seem right to me.