Rear axle seal

Hi 2CarPros,

I just read through your detailed description of the removal and reassembly process for changing the rear axle bearing and seal, which was very informative. I recently changed out my brake pads and rotors on my 1500 LT truck and I noticed that the inside of my rear driver side disc brake was caked with a gray (graphite-type) grease. I have come to the conclusion that it is my axle seal, please correct me if I am wrong? Unfortunately, I do not have any pictures. Since I bought this vehicle used, do you think it would be the best practice to replace the axle bearing at the same time as the axle seal since I do not know if they have ever been replaced? Since I have got the rear differential open, do you think it is wise to do both sides as well? I recently bought an axle seal and bearing kit from 1AAuto which comes with both right hand and left hand bearings and seals for $45.00, so I will have both sides on hand if needed. Ultimately, it will come down to a visual inspection of the bearings and axle I am assuming. Any insight would be greatly appreciated!

Thank you in advance,
Tyler