Mercedes 2017 Sprinter 3500 DRW rear axle flange leaking oil

My Sprinter is showing a bit of oil leakage from the rear axle flange and as a result is slinging the oil out onto the wheel. It's not a real bad leak but enough to to make you wonder if something needs repairing, I've been told by another Sprinter owner that he had the axle pulled and had silicone applied at the axle flange surface and problem was fixed. I was also told that the problem was not a leaking axle seal. Not sure what causes this leak or how to repair it. Any thoughts? Mercedes wants $3,100 to replace the seal but this was strictly a quote over the phone without looking at the problem.