I just received my RNS-E today and upon opening it, I noticed that there's a piece broken off the back of it. Can you tell me if this is a big deal or not and what potential problems it could cause?
Don't worry about that broken piece. A lot of used units have it same way.
Those plugs are too close to each other so if you doen't use dual connector you need to push it hard (mostlikely brake it anyway).
It doesn't change usability in any way.
The broken.jpg shows a broken Fakra connector for the diversity antenna. usually happens when you press an SMB plug to strong onto the Fakra connector. You may be fine if you get a dual Fakra housing for your antenna since it's still hold by the main antenna which seems to be OK.