Re: Under Glue streaks/marks on leather dash?
Leather is not the most practical cover material for a dash. It tends to dry out in hot, direct sunlight, which can cause it to curl up and shrink. And because it is somewhat permiable it can allow for glue printthrough, like on vintage wine labels stored in damp cellars.
I am no expert on leather, but seemingly a more suitable tanning chemical would help. (Not a solution is what is often used for tanning in India and other poorer countries: urine. That would really piss people off.)