Hydraulics Question Long 510

[luvmexfood]

The 3 point hitch arms became jerkie and would whine when trying to lift. Checked hyd fluid and it was a little low so I added about a gallon. Still same problem so I thought maybe some air had gotten into the system. Opened a plug and the fluid that came out was the color of cream maybe just a little more yellow.

I guess water has gotten into the system. Can I just drain system and install a new filter or does it need to be flushed somehow?

Any advice would be appreciated.