Duffer

Lexol, Zymol, Zaino, used 'em - sticking w/Zaino for now and old toothbrush to get to between seams

My Blu TT

I am typing this up from the Griot's Garage Detailers Manual.
"There are two types of leather: vat-dyed and sprayed-on leather. With vat-dyed leather, the color is obtained by immersing the hide in dye. With this process, the color penetrates completely through the leather! With sprayed-on dyed leather, the color is "painted" on. While this produces a more even color, some of the natural grain of the hide is lost and the overall life of the leather is diminshed. Normally a painted-on dye will wear off at the stress points. (You may think this is just dirt buildup, but on close inspection the painted-on dye will be gone!) No matter how hard you try to clean theses cracked areas, you can't clean the area where the dye has cracked off. If you own a European car most likely the leather is vat-dyed (yeah!). U.S. and Japanese manufacturers tend to use the spray-on dyed leathers (boo!)
Before treating any leather with Leather Care or Leather Rejuvinator, use Interior Cleaner on the leather the same way you would vinyl. In fact, Interior Cleaner is safe for all the surfaces in your car. After you've cleaned the leather examine it closely. If the leather is old, stiff, dry or cracking, our Leather Rejuvenator is your best solution. While it may temporarily darken the color, it's penetrating formula will rejuvinate and soften the fibers deep down in the leather. After a few days the area will lighten a bit. Test a small area first to ensure you are O.K. with the look. If the leather is newer use our Leather Care. Both products are applied the same way. These products are different than the lanolin-based leather products. First, our oils can penetrate deeper than the lanolin-based leather products, and if you have any perforated leather, our leather products won't leave behind a white residue in all of the perforations. And don't worry about getting water on your leather interior. It won't hurt it as most leather is tanned in water!
Apply Leather Care using a Blue Detail Sponge or our 100% Cotton Polishing Cloths. Apply the product to your applicator and wipe the surface, rubbing the product into the leather. As with all our car care products, don't use too much: a little goes a long way. Allow the product to sit on the surface several minutes. Now using a clean cloth, wipe the excess product off. For a deep feeding of Leather Rejuvinator, apply a liberal amount to the leather and let the product soak in overnight if possible. (Sometimes I've found my hands to work better as they keep the product warm and I can massage itinto the leather as well.) If you are not going to be driving the car soon, repeat the application of Leather Rejuvinator if possible. You'll notice the leather getting softer and softer with each application. Keep the windows cracked so any excess evaporating product can circulate."
<phew>
I know it's very "product" oriented, but I use their stuff in very hot very dry weather with excellent results...
So take it for what it's worth.
Brian