Sorry, but I've not had chance to reall the whole of this thread but...

Have you had a look at the relay module internals? (I posted a pic here somewhere) If the relay is the problem then you will almost certainly be able to repair the old one - there is virtually nothing to the module, just some open frame relays and some diodes. The most likely problem is a hairline crack around the relay pins on the PCB. If this is the case then resolder it. Then you can send the new one back for a refund. HTH.