Hopefully Gerald J. will chime in and further describe the issues and what tractors this covers. (pre side console) and any other pertinent details.
http://talk.newagtalk.com/forums/thread-view.asp?tid=438400&posts=1#M3528181
I had his page bookmarked as similar issues have been inquired about before.
http://www.geraldj.networkiowa.com/4020si.htm
John Deere 4020 hydraulic problem
