Get this. http://www.colorplus.com/
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).
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)