I hear:
"The leather under my butt looks loose,
do I need more padding?"

The Fiero seat has a "Perimeter Frame".
There is no support in the center of the seat.

Sometimes the foam tears.
In which case you will sink below the frame,
this will make the leather look like it needs more padding.

If the foam has torn on one side,

 you can be sure it has torn on the other side too.

Here you can see how if the foam has torn,

  you will be sitting on the floor.

To support the center foam:

Here  5  strips of "Plumbers Tape" were added to this seat.
  (thin metal with many holes, sold as a roll, costs like a buck)

Use sheet metal screws into the metal under the tracks.
  (don't weld, you will set the foam on fire)

Do Not cover the small holes along the seat sides
  where the upholstery hog-rings to the frame.

< The Red Arrows show where these holes are.

The owner of this seat weighed 275 pounds.
   Shown above is  5  straps were added.

For someone less heavy  3  straps are recommended.

If you find this torn foam AFTER the upholstery is installed,
  you DO NOT need to completely remove the upholstery:

1. Remove the tracks.
2. Remove enough side hog-rings to install the straps.
3. Re-assemble.

Once the foam is properly supported the seat is as good as new.