Still High Iron in my 914

Are you using AeroShell Sport Plus 4 Oil?  Very important to use correct oil in 9-series engines where crankcase and gear reduction box share the same oil....

Yes, absolutely.  I've only ever used all the proper Rotax-recommended fluids.

We compared your oil analysis to another Rotax engine and your iron content is very high. We recommend you send your gearbox to a Rotax service center for inspection (Make sure to include the small drive gear on the end of the crankshaft). Please make sure you use the correct oil (AeroShell Sport Plus 4), and that your carburetors are balanced properly. Unbalanced carbs will cause your engine to vibrate, resulting in excessive gearbox wear (same with an unbalanced propeller or weak engine mounts)

Here is a video on how to remove your gearbox - https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/298-gearbox184

Here is a video on how to install your gearbox - https://www.rotax-owner.com/en/videos-topmenu/expanded-video-instructions/392-replacement-of-the-propeller-gearbox-sb-912-056-914-038

Here is a video on how to check your friction torque on the gearbox - https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/60-friction-torque29

Here is a video on how to sync your carburetors - https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/43-carb-synch17

Here is a link to Rotax Service centers - https://dealerlocator.flyrotax.com/

Do you think it would be OK to get the carbs balanced (and maybe the prop balanced too) and see if I'm still generating iron in my oil (fly for 30 hrs) before taking the step of removing the gearbox (which I wouldn't do myself)?

I do use Aeroshell Sport Plus 4 Oil (I always have).

You can try that and see if anything changes. If the iron content increases or remains the same, then we would recommend sending the gearbox to a Rotax service center for inspection.