I have 2018 3901WB and replaced all valves with Valterra valves and cables and they work great. The problem is the routing of the cable without attaching them properly and avoiding tight bends. I simply drilled new cable holes as needed to route them properly. Drain tanks completely before starting and use the level up to slant the trailer to keep stuff remaining in the front of the black tanks. I found that the valves in my trailer were installed improperly causing the rubber seals to bind and leak making them hard to operate. After I was done I couldn't believe how easy they operate and have since. Unfasten and bend the color-plast as needed for access. If you have to cut access holes keep them square and three sided with the remaining attached side toward the front of the trailer. Then use 1x3 pine boards to secure the color-plast in place with 1/2 screws by mounting the boards above each gap to to close them off and allow for reuse for other repairs. Not that tough once you get into it. The hardest part is putting the new valve seals in right so they seal. Once you get them in right the valve will open and close easily by hand before the cable is installed. Good Luck!
2018 Redwood 3901WB pulled by 2016 Chev 3500 HD DRW. Goodyear G114 tires, Moryde I.S., Kodiak Disc Brakes, Splendide W/D, Tire Minder TPMS, Sleep # King.