Buying a backhoe loader. What does this dirty rear diff mean? is this thing leaking?

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Hey all. I'm new to backhoe loaders and I'm trying to purchase a used backhoe loader for my projects building a few houses. I am looking at a very rusty CASE 580 SM. test drove it the other day but I need more convincing.

The imgur link above has some of the photos i took of the case 580sm backhoe loader. its rusty and im worried about the carriage underneath. That rear diff looks dirty but it wasn't dripping. what...

Buying a backhoe loader. What does this dirty rear diff mean? is this thing leaking?

Buying a backhoe loader. What does this dirty rear diff mean? is this thing leaking?