I abused my 4wd tractor. I paid the price: First sign was what you see. Just figured a leaking seal on a 10 year old tractor. Then I noticed the wheel hub casting started separating from the axle gear casting, barely noticeable at first and over a few hours expanded. When it got to one quarter inch I figured I had a problem.
I did, the abuse broke one of the balls in the main wheel support bearing best I could tell. This metal ball remnants got into several things and started eating up parts. Result was $600 worth of parts only, I did the work, for both sides. The other side wasn't showing but I decided to open it up and check it and glad I did as it too was damaged but I caught it before the damage was as bad as the one that caught my attention.
So, sir, my advice to you is to check things out. May be time to drain your oil anyway. On mine, pop the wheel and the casting with the wheel studs has about 12ish bolts in it. Removing them allows you to remove the wheel/gear drive assembly. All my problems were in that assembly which was a rather simple bench repair operation. Had never been into a front end and had nothing but the parts diagram but that was enough to identify what failed and get the right parts.
The owners manual said to use the same fluid in the front axle you used in the main sump. The knowledgeable guy at the Branson parts warehouse in Plainview, TX. said that i should be using 85w-140 in that front end, not what's recommended in the owners manual.....printed some 10 years ago when I bought the tractor....apparently in that time things have changed. The 2016 2400 I bought last year is only 24 hp, not 65 but it specs 90w for the front gear box. They had all the parts I needed to make my repairs in stock and I had them in about 3 days.