you knew before you got the bag that it wasn't an ortlieb.
was it really until recently that it wasn't waterproof, or were you just not that wet before?
spend the $10 and get some seam sealer and then spray the bag with scotchguard.
i too have a midpack and i love it. there are sometimes that you have to accept that a bag made of cordura, thread, and nylon with non-high frequency welded seams is not 100% waterproof.
if you really have to, carry a plastic bag/dry bag for when you need to carry a document in the rain. this absolutely does not merit reload paying the shipping back for you, or a replacement product.