We prove that all extensions of K5 have unary unification, even with parameters. Our proof is constructive in the sense that we can effectively compute, in 4-exponential space, a most general unifier for any unifiable formula. In particular, this proves that unification and admissibility are decidable. We also investigate special unification types: we show that K5 and KD5 are transparent, and we characterize the projective extensions of K5.