Do you use a Drain Master electric dump valve?

PPL Has Auto Drain Kits. The kit is a motor assembly as noted above, not a complete powered valve assembly. Description says it fits Valterra and Bristol valves. I like the idea of the valve and motor being separate components, can replace one without the other. Still, at the price I think I'd go with new cable-equipped Valterra valves. They're about $50 on Amazon. A little more for 3" and a little less for 1-1/2".
We have those Valterra valves (72" cables), and they're 12 years old, stiff but still working.

i should add
ours does not use a cable
the motor and gear mechanism replaced the pull handle, and is mounted at the valve
the open close switch is mounted in the compartment

I had a similiar problem as you have where the valve was hard to operate and it turns out the seals were swollen due to my using the wrong lubricant on them. Use only the silicone lubricant and not any with a petroleum base.

Thanks for your replies. The valve is not accessible so an Allen wrench will not help.
I think I am going to start with new seals. Today I removed the Velterra cable that runs to the valve. It had some kinks in it. After straightening out the kinks and putting some silicone lubricant in the lining the cable was very smooth. After hooking it back to the valve, it was hard to operate again. So, I think something is up with the seals. Very difficult to close the last 3/4" or so. They are adjusted correctly.
I ordered some tank valve lubricant and will be using it in both my black and brown water.
Ben

Some tips that helped my friend with hers were; Exercise the valve at least once a month. Use valve lube in your waste tanks. Have the vehicle running when you attempt to open the valves, as the slightly higher voltage can make a difference.

I would add, carry the proper Allen wrench for manual operation.

We have one called "Auto Drain"
It was on the RV when we got it, it's way old, and always works
No idea of who the MFG is, but was probably sold at camping world at one time

I have a friend that has or had them on his Artic Fox. Last winter at Yuma, AZ. the black tank valve went belly up, went on line and the only place to buy the valve that we found was from the manufacture. Of course it was a PITA to get to. Then shortly after, one of the gray tank valves bit the dust. He now is modifying for cables or some other way for opening. I did notice something while helping him, it was noted to place the pull opening at 10, 12, or 2 0'clock. Well that means closing the slide will work from the top down. When dumping tanks you know anything that doesn't come out will fill the slide slot at the bottom.

I had them about 10 years ago, and I had to remove them as they were very prone to not opening. May be better now, but I won't be giving them any more of my money.

I have had two Drainmaster valves but didn't use either one. They didn't work. They worked great until there was liquid against the valve, then they would not open. A real problem on the black tank. This was years ago so if they are still in business they must be better now.