I don't know if this is true for all early tanks vs. newer tanks. I recently bought a non running 86GT. It had the smaller/older tank. This car sat for 10yrs, the tank was rust except for a shell of nice exterior paint. The outside looked great, Interior was horribly rusted. I went to a radiator shop in town to have it cooked and sealed. They said with the plastic baffle that they cannot do anything with it. I have a totalled 87GT in my back yard, I felt too lazy to remove it at the time. However with no tanks available I removed the 87GT tank. It has sat in my back yard for 5yrs. When removed there was not one speck of rust. I made some new brackets for the larger tank to fit into the older fiero. They changed the mount locations. If I were to look for another tank I would look for the 87 or newer 11.7gal tanks. It appears that they had a different treatment on the inside. Others may correct me, just my recent experience with no statistical data. I did look at around 5 pre 87 tanks before pulling my 87 and they were all rusted garbage.