Until you have a leak due to bad seal and grease breakdown, no maintenance is needed. Except maybe a small lash adjustment if it gets sloppy and not attributed to worn steering parts. I have rebuilt 4 Corvair manual gearboxes and repack them with Royco 81MS grease or John Deere Corn Head Grease AN102562. 2 more on my bench wiating their assembly turn.
I don't know if the Camaro manual box is like the Pontiac's box but here is a link that describes its rebuild. Looks similar to what I did on the Corvair gearboxes. Smaller steering shaft on Corvairs is the main difference that I can tell.
If you look closely (see attached), it actually says "CHECK LUBE" with two arrows pointing to the bolt you remove to check the level. Your "CHECK" is a bad casting so your question is understandable. Even though it's rarely necessary to add anything (unless you have a bad seal as previously stated), the service manual states to check it every 36k miles and add water resistant EP chassis lubricant until it appears in the outboard screw hole (see below).
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