The slippery stuff causes mating surfaces to slide back and forth even more, which will create noise.
What you need is to make the surfaces (leather, rubber) as matte and supple as possible, which means using quality conditioners, nothing like armor all.
Once you get the surfaces matte and soft, the noise should greatly reduce.
Personally, I love Leatherique and Einzeit Cockpit. I use the Einzeit on the seals and it works great.