Faulty parts sold over counters with no warranty.

I am the owner of a 2009 335i Sedan and I was sold a faulty waterpump on 25-10-2014. The dealership is refusing to refund or replace the leaking unit under warranty as it was fitted to my car by a fully qualified friend of mine and not the dealership itself. They claim that the standard 2 year warranty does not apply to parts sold over the counter, not fitted by the dealership, but they do not inform customers of this, not verbally or even on the invoices, where it is only indicated that \parts supp**** correctly is not returnable""; to alternatively support respectable suppliers such as Goldwagen and Midas instead; not only for selling higher quality parts for much; much less; but more importantly; including a 1 year warranty; regardless of fitment. Mr. du Toit;I want a refund and I look forward to never doing business with BMW again. It might just be time for an S3. """