I use Ekamold EP Boron Nitirde spray on my slumping molds. I am noticing a cloudy filn on the glass after slumping. I have washed the glass in soap and water as well as with Oxyclean and soaked in oxyclean but it does not seem to come off. I fire using the pre-programmed slump schedule on my Evenheat kiln. Some of the elements are starting to pop out, not sure if that is related.
Stick with MR-97, which is made specifically for glass.
The first BN spray I bought was Hi-Temp 1800. It left a haze on the glass, and I had some glass stick to a stainless drop mold. My opinion is you will have much better success with MR-97. I tossed the can of HT1800 and exclusively use MR-97. I no longer have problems with sticking/hazing.