I bought a new jack hammer. After using it for a few hours grease started to come out where the bit is. Is this normal

No thats not normal real JACK HAMMERS on AIR ??? but its not Milwaukee not Bosch not Dewalt but a China brand? if you are have a real jack hammer then its not the right collum because its placed under Hammer drills? and you have also not possible speaking about maybe a little weight rotary hammer ? because ONLY real demolition and jackhammers are very specially made for the long lasting jobs !!! but the weight and power is very important by use the right tool for the right job the most rotary hammers ( exept brands like Hilti and Duss) are not made for long lasting jobs and are made for only working for a short time. its also makes the great price difference between a hammerdrill a rotary hammer a real demolition or a real jackhammer is much higher price. The tools on air Atlas Copco or Ingersoll for the hard and heavy jobs
If you have bought your tool by a hardware store and it is a real jack hammer go immediately back its possible that you are wrong informed by the seller or the budget was the fact. about the price for the tool maybe you have a real jackhammer but have choose a to little model size machine to do the job or its a budget brand online bought China machine. Its a simple question but a hard answer, difficult questions do not exist but difficult answers sometimes.
Regard and luck by warranty and a very small change maybe it is just only a factory flaw.