Eastman Speedflex valve question

I'm renovating a bathroom and have 2 BrassCraft valves and 1 Eastman Speed Flex valve which controls the toilet water flow. The Speed Flex valve is leaking around the stem in every position but full on or full off and has a slight drip in the full on position. I can't have that so I took it apart and cleaned the stem assembly hoping that would work, it didn't and actually made it a bit worse as I cleaned away the crud on the stem. I noticed in the stem assembly near the screw on nut that there is a thin metal washer but no rubber washer in behind it. Is there suppose to be a rubber washer there or not? If not how can I get this rascal to stop dripping?
If there is suppose to be a washer there can I use one out of a Brass Craft valve which almost identical valves but not quite?
I've got it in the open position and it's holding for now but I don't trust it.

Please note this is not the rubber washer on the end of the stem that sits inside the valve body, that one is there and is in fine shape.

I thank you very kindly for your time and replies.

Chris

I'm not a professional, so the fact that I've never heard of this kind of valve means very little. I would say however, for less than $10 you can buy a brand new 1/4 turn valve for your toilet and that will cure the problem. Repairing relatively inexpensive valves is, in my opinion, largely a waste of time and will save you very little if any money.

I like replacing shutoffs that are 20 years old or more.
They don't last forever, and parts?
For a five dollar valve?

valves

Many of those valves are "generic" regardless of the brand, and the stem from a new one might fit the body of your old one.