This is the correct answer i wouldn’t go hammering it as mentioned by OP. Like in a carb there are passages that are drilled after casting that have welch plugs in them to block them off where needed.Just a wild guess, but it may be there to seal off a passage that was required during the manufacturing process but no longer needed for the part to function. I've seen this on throttle bodies before, where they fill a drilled hole with a steel ball and "stake" the aluminum around it to seal it in place. Again...purely a guess on my part.
So if I did hammer it and it went down a bit could it affect anything. Worried about the spaces around the ball. They happened after the hammeringThis is the correct answer i wouldn’t go hammering it as mentioned by OP. Like in a carb there are passages that are drilled after casting that have welch plugs in them to block them off where needed.
Yes you likely broke the seal on the plug. i believe there are two set of passages in that part of the drive. One is cooling water through the drive and into the bellhousing and then up to the engine. The other one is the gear lube up from the lower half. Normally these passages are made by drilling in from two different angles and the plug blocks off one of the drill holes. Hard to say what it is without the drive in front of me, but best to hide the hammers from your self until you get it back together...
They stay open. Most grease zerks are open, wouldn't hurt to put caps on them. I'd think the caps would fall off on the u-joints from spinning around that fast.