joey400ex

Noticed loud grind/knocking noise from left hub (front drivers side) after using 4x4 through deep mud hole and when I went back to 2x4 is when the noise start. I figured the wheel hub was going to lock up so limped it home and made it. The noise did smooth out the closer I got home (45 minute drive). I assume the hub needs replacement, but I took the wheel off and there was mild play in the hub bearing. I did notice the insertion point of the front axle and looked like something was missing in the housing where the shaft inserts. The passenger side has a plastic piece whereas the driving side has nothing. Is this normal and should I be concened? I am very new to jeeps and was curious. I have not checked the fluid level in the front diff yet but plan on working on it more in the next couple of days.