Hey, Andrew!
I think OEM is the way to go. URO does not have a good reputation for the quality of their parts. Most of what I've heard in that vein is about their tie-rods, but that makes me think the new failure you are experiencing is also due to the part.
If price is an issue, there are several local Porsche boneyards that will have used relays on hand. They were used in a lot of different Porsche models through the years.
You may want to double-check the current flowing through the relay. You didn't say if the problem was the switch part of the relay or the coil, but if you get creative with wires and bullet connectors you can make a test harness that would let you check how much current is actually going through the part that burns out. I'm frankly not sure how much should be, but if it is very high you may have an underlying problem that is causing the relays to die.
--DD