Silicone based sealant on silnylon
McNett Seam Grip on everything else
But, I sometimes use silicone based on non silnylon. It doesn't turn white and flake off. It turns clear. It tends to peel off over time, especially in high abrasion areas.
If you've put silicone on and there's still residual, the McNett might not stick. Maybe clean it off real good with mineral spirits?
Did you use mineral spirits (paint thinner) to dilute?
Permatex Flowable Sealant comes pre-diluted and is supposed to be stronger.