Best lube for grey tank and black tank valves

My valves started moving hard when my current MH was about a year old. I coated the blades with Silicone grease. Made the valves work very smooth and have stayed that way for the last 4 years. My previous 2 MH's never had the problem.

I used this: MPT19 Silicone/PTFE High-Performance Lubricant