Leather work is a lot like auto-body work only softer and something you can do indoors. I am not affiliated with any business. I can refer you to a company that I've had good experience with, another Imperial owner's experience, and what I've done.
The company is called Leatherique. They are decades old, they hold the patent for the aniline dye process. They publish an informative book they posted online that explains how to clean leather and how their collagen products have a capillary effect which would take out that dirt you see on your seats.
http://www.leatherique.com/2011-leatherique-book.pdf
They sell a cleaner/conditioner set which is largely collagen in two viscosities. They color match dye, tho I understand some reds are more difficult nowadays.
1964 and 1973 Imperial owner, Kerry Pinkerton did a good write-up of his leather restos on his 2 Imperials using Leatherique's products. Some of the photos in the 1973 section are like double exposed or something strange, but they are fairly informative. He had split seat covers and he used the time tested method of gluing in a suitably sized piece of vinyl, with the cloth backing side up, to either side of the split seam and bringing the two together. The end result would make you think it took real work when its really easy.
Refinishing (Chrysler) Imperial Leather Seats by Kerry Pinkerton
I have used their products on a lot of Imperial seats, specifically my 1964 Crown Coupe seats which had old style, thick hides. I learned a lot on those. I sanded off the old dye when I didn't really need to but in that I saw how much abuse, like coarse sand paper, leather like that can take. That gave me confidence to go at lesser leather and I've had good results with leather furniture and more modern leather in cars.
My claim to fame is to go one better than what Leatherique's book describes. They say to leave the car out in the sun with the collagen conditioner on the seats so it warms up. I saw a garment steamer for sale on Craigslist one day and bought it. I used the Leatherique cleaner directly in the steamer. Eventually it clogged up the steamer but that was ok, it was only $35. I see them at Walmart for about $50-60 new. I like the garment type as it has a long hose and a hanger for the hose which makes in-car cleaning easier.
The primary benefit of the heat is that it gets the cleaner up to a heat that unwinds the 3 strands that makes up the collagen molecular structure. This unwinding causes it to become thinner so that it more effectively gets down into the pores of the leather. As it cools, the strands try to recombine which lift up the dirt and oil from the pores in a capillary effect. This is explained in detail in the Leatherique book in the link above. The overall method is that you put down the conditioner over the leather, then apply the heated cleaner over it. When enough wetness starts to pool up of this hot solution, a towel is used immediately to gather up the oily grime before it can sink back into the pores. Its very elemental and its THE WAY to clean leather. You can't get this with soap and water, you can't get a clean like this with Armorall, etc. This is applicable to all leather in your car or in your house.
Its not cheap but its cheaper than finding new seats, and you keep your Imperial original, and the cleaned leather looks, feels, and smells just like new when used in this method.
Your seats look pretty easy to do from my experience. Coming at it from a novice standpoint, you'd be surprized at how well you did after not too much work. The seat covers come off pretty easy from those seat frames but I think you can do everything in the car from what I see.
Ask if you have questions. Thats a freakin beautiful car, the red leather and black paint is one of the best combos on those Imperials.
