Get this.
http://www.colorplus.com/
The Softener. I use it for my 10/87 build E30 3 series. If you want I can provide pics of my 25 year old interior
These guys are experts. I've toured their facility a few years back & I highly recommend them.
I don't use their stuff on my E88 because it's still practically a new car and the seats don't need much more than a basic quick maintenance product used regularly (*I'll probably use the conditioner next year though).
__________________
Jimmy
1988 325i sedan (Cirrus Blue Metallic, Silver Grey Leather)
2011 128i convertible (Blue Water Metallic, Grey Leather)
2013 320i sedan (Sapphire Black Metallic, Black/Black)
2016 228i convertible (Mineral White, Oyster Leather, Luxury Line)