I have a 4940C I got in the cab the other day and when I sat down on the seat it broke loose from the mount. I went to see what broke and found the back of the suspension system had broken loose from the mounting frame. I took the seat out to see what had broken and found that the brackets that secure the back part of the suspension system to the mounting frame were made of plastic and both of those brackets had broken. In my case I had just gotten into the tractor and sat down when they broke. If I had been doing something with my front end loader when it broken I might have had another front end loader boo boo to add to the list. Rather than try to get new plastic ones. I just made some out of 1/2 inch steel that I had available. I dont know if they changed the design on that part of the seat or not but you might want to check and see if yours are still plastic.
If you look at the suspension system on the seat you see a round rod sticking out of the suspension system on each side in front and these are inside a rubber roller. The back has the same rods sticking out but they go inside the plastic mounts to secure the back part of the seat in place. It is not a hard fix and manufacturing the new brackets are not hard. I had some 1" x 1/2" steel available basically all I had to do was cut two pieces 2 1/2 inches long drill a 1/2 hole for the seat to fit through then drill and tap a 5/16 inch hole on the top and on the side to mount to the frame.