This assumes that deontological rules must be unbreakable, doesn't it? That might be true for Kantian deontology, but probably isn't true for Rossian deontology or situation ethics.

We can, for instance imagine a deontological system (moral code) with three rules A, B and C. Where A and B conflict, B takes precedence; where B and C conflict, C takes precedence; where C and A conflict, A takes precedence (and there are no circumstances where rules A, B and C all apply together). That would give a clear moral conclusion in all cases, but with no unbreakable rules at all.

True, there would be a complex, messy rule which combines A, B and C in such a way as not to create exceptions, but the messy rule is not itself part of the moral code, so it is not strictly a deontological rule.