The bottlenecks were DOH-SYD, supposedly no D class available in the first two weeks in October. I'm booked end September now, which is fine.
The other strange one was SYD-AKL-SYD on LA800/LA801 where again no D class available in October. I'm now booked on QF metal BA code for these segments.
I always thought D class is not particularly scarce as it is revenue and not deep discount (except of course in the case of ex-CAI

).
Anyway, I'm all sorted for now, just wanted to share the experience and indeed may go for the AA RTW desk for any future changes.
Thanks for your input and help.
I'm seeing D9 on pretty much every QR908 flight in the first week of October. But it could be some weird married segment logic.
Glad it's all sorted. ^ ^