My 4230 keeps slipping out of park.
I have followed the instructions to adjust it but no luck
It seems that it just isn't "over-centering enough to move the lever on the housing enough to keep it engaged
I am assuming you have the powershift transmission? If you can't adjust the cable enough to get it to hold, something is probably broken inside unless the linkage under the shift console is worn and not shifting far enough. You will need to take the top cover off the transmission to look inside. Could be some teeth broken on the park pawl or pivot shaft could be broken or out of place.
I know that it started about the time I was loading a truck with hay and I could not get the tractor to move from the forward gears to neutral or reverse. It finally did move after some struggling but afterwards I started having the park issue. is there access through the cab floor to see what you are showing?
There is a removable plate in the floor to get to the transmission cover. not much can be actually repaired from the top. Most likely the cab will need to be removed to repair, if linkage is not the problem.