One of the first things we check when it comes to your hydraulic systems is the fluid. What are we looking for? If the fluid has not been changed in a long time, it begins to break down and does not have the consistency for your hydraulic system needs to work properly. We are also looking for water in the system that would cause it to become a yellow foamy fluid instead of almost clear. There are two ways for water to get into the system. The most common is simply the engine heating up the fluid and condensation begins to form over time. The second is through worn shift boots and seals. Either way, the system needs to be drained and replaced or risk possible pump failure.   While we are on this subject, we need to talk about the older John Deere tractors out there. Most tractors will run hydraulic/ transmission fluids. John Deere tractors do not and need the higher grade hydraulic fluids found at tractor supply and other stores. It is basically a refined 10W30 motor oil. If you run the other, it will look like snot and plug the hydraulic filter. On my 2010 John Deere, I put in the Tractor Supply 303 hydraulic transmission fluid and it became so snotty that it not only plugged the washable filter, it collapsed it costing me some $$$ for the filter, flush the system with Deisel fuel, and put all new high-grade hydraulic fluid into it. It was an expensive learning lesson.