These are two different issues.
Issue 1 is the bridge:
Early Rickenbackers do not have screws in the back of the bridge, so over time the tension of the strings can lift the back of the bridge away from the body. This was corrected sometime before 1987 with the addition of two screws at the back of the bridge.
This bridge has the extra screws:
https://kitarablogi.files.wordpress.com/2012/12/rickenbacker-4003-e28093-bridge.jpg
This bridge does not:
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If the bass you are looking at does not have the extra screws, you will want to make sure the back of the bridge is still flat against the body.
Issue 2 is neck separation:
I have seen an instance of the neck separating from the body wings at the front of the body at the joint, where it first meets the neck. I subsequently heard that it is a rare but known issue in older Rick basses. A guitar tech told me that it can be stabilized, so it might not be a big deal, but it is something to be aware of.