What year is the 4020? Those prior to 1969 had the cross-type grip on top. My 64 has a cast steel top, my 68s have a different metal, maybe aluminum. As for it not threading tight, have you checked the treads? More than one has stripped out over the years.
New ones are available from Deere.
If you post a pic and the serial number, someone here will be able to tell you if you have the right one.