Hm, I don't know that this entirely satisfies me. For the first two lines, it seems like both "voice" and "tears" are compared in terms of "existence-apprehensibility," sort of: "I hear your voice, but I don't see your tears". I feel like "cannot be seen" makes it seem like the tears are around, just not visible, whereas in reality the poet is trying to say that there are no tears. (This one is a bit YMMV, I guess.) For the last two lines, it seems to me that what the poet is trying to lend is the soaking-wetness of the sleeves (hitsu o), or (one step removed) the tears that have soaked them ("you have no tears, I have tears to spare; help yourself, man") -- not the sleeves themselves.

Just so this won't get completely nitpicky -- I like the c/c/c and then s/r/b - s/b/r sound patterns! --Matt