I notice good bit of Dirt on the undercarriage and the Differential Cover leaking at one of the Bolt's.
Although it is not in the Service Schedule, the Axle Air Vent need's to be taken out, cleaned with Diesel Fuel and Blown out with Your Air Compressor to make sure that that it is Free Flowing, every so often depending on usage environment. I take mine out every year or so to clean it, but I try to check it @ Every Oil change. My Tractor get's a Lot of Dirt, Mud, Etc and has multiple Air Vent's ie Axle, Transmission, Hydraulic Reservoir's. I take them out @ Every Oil Change, Clean them out with Diesel Fuel and Blow them out with the Air Compressor. Dirt Dobber's and other Insect's can build nest's in or around the Air Vent's causeing them to Clog or Partially Clog. My Tractor is 4x4 and the Front Axle Vent Early on was Clogged by Rust and Dirt Accumlation. I had to use a Wire along with Diesel Fuel and Air Compressor to Clear it out. I was lucky to catch it in time before the Axle Gasket's got Blown out and started to leak. Cleaning the Tractor Air Vent's wasn't in the Maintenance Schedule either.
The Leak @ the Differential Cover may be because of Excess Air Pressure in the Axle Houseing caused by a Clogged or Partially Clogged Axle Air Vent. The Axle Bearing Oil Seal's can also be affected and cause them to also start leaking, which will require them to be replaced to fix the Oil Leak.