Sorry, but I can't help myself....I've spent too much time over the years getting worked up about the flimsy suspensions under the later crop of air seats to sit this out. 

Look at the linkages under a Hydro-Cushion or Magnum and compare it to the Grammer crap that was all the rage after it was discontinued, and also installed on other brands while the HydroCushion was out.  There is absolutely no comparison....Grammer: welded together from half inch strap.  Not very wide.  Not very good welds.  Lots of lighter stamped sheet metal parts with every part seemingly dependant on one critical little piece of plastic that keeps it all together.    HydroCushion:cast steel, wider.  Grammer:  Height and weight adjustment is a joke on the air rides, and even worse on the spring rides. HydroCushion:  Simple lever on RIGHT for height and simple lever on LEFT for firmness.   Weight is self adjusting. Durability:  Grammer: You're lucky if you have one which isn't broken at 3000 hours, let alone 6000.   HydroCushion: well, after 6000 hours on a tractor which is somewhere between 25 and 28 years old, it might need the accumulator replaced.  Parts for the Hydrocushion will be in the parts book and on the shelf at he depot if not the dealer.  Good luck finding any parts availible for an early '80's Grammer seat....I've done the NewHolland/Caterpillar/Steiger/Versatile shuffle trying to find someone who actually had individual parts for one from the '90's.   Grammer's shock absorber requires contacts in high places in Gabriel to even have a chance of locating one. 

There's a reason that FNH has a complete replacement seat from Sears in their parts flyers all the time to replace the throw-aways they installed originally.