As has been stated before and in other threads, oil based preservatives can soften the glue that holds the rubber rands onto the leather. I have used obenhaufs before and experienced it first hand. As for leather conditioners/waterproof cream, my favorite is Zamberlan hydrobloc which is water based.
I have used Obenhaufs, Nikwax, Kenetrek Montana Pitch Blend and the Zamberlan Hydrobloc and the Hydrobloc is the best by far IME. It seems like the leather likes it - it seems to soak it up and as a result the waterproof qualities seem to last longer as well.