I have noticed that when I ride in the passenger seat of my 69 with a bench seat that I sit higher than when I am in the drivers seat. I assume its because the springs are worn more on the drivers side. Is there anyone that sells a new replacement bottom bench seat spring assembly? All I have been able to find are the bucket seat spring assemblies and lots of replacement bench seat covers and foam. I have read through lots of old threads here and read that extra springs along with extra, more firm foam, can be added to stiffen up the area that has become weak. Where do you find new springs to add?