JD 455G Transmission

I started up my 455G loader after a couple months sitting. After a few minutes when I took off the brake I got the transmission pressure warning and the stop light and siren so I shut it off. Looked at the transmission fluid and it appears to be milky with water mixed in it? I ended up preparing to draining the fluid and replace the transmission fluid filter but when I removed the filter it was only about 1/4 full of fluid which I found odd. Is there a pump that might be not allowing fluid...

JD 455G Transmission

JD 455G Transmission