Welcome to the forums SaminPgh.
I have a GGW-H20L, which may be close enough for me to help. I've used Verbatim brand BD-R discs with no issues. And now I'm using Smart Blu discs made by FTI, with the mid code TDKBLD-RBB-000 with very good results.
If you are in the US, you can find the Smart Blu discs at mediamegamall.com. They are a bit overboard on shipping/handling when ordering small amounts, I must warn you.