Toilets, Sinks, Showers, Tubs and Disposals - Repairing a leaky 3 valve diverter

I have a leaky diverter which is causing water to come out of the tub spout even after turning the diverter knob to shower, causing low pressure from the shower and wasted water from the tub spout. I have removed the knob cap by unscrewing the philips screw at the front of the knob. Now I see a threaded stick in the middle of the pipe. What part need to be replaced to fix this issue and how do I remove that stick if needed to. The fixture is the original from a house built in 1952. It has the three knobs lined up in a row with the diverter in the middle and hot/cold on each side. Please help! Thanks in adance.

Wow, you were lucky to even remove the faucet handle.

Once the handle is off, there will be a chrome piece. Remove it. Then you will see a small brass nut with a brass rod sticking through it that the handle mounts to. That is the packing nut. Behind that nut you should see a larger brass piece that you can get pliers or a socket onto. That is what holds the stem assembly together, into the valve. You will need to remove the stem assy and replace the washer on the other end. Also check the seat inside the body of the valve. If it is not smooth you will need to replace that also. Special tools may be required to do this project.
You will not need to shut off the main water as long as the hot and cold handles are holding. If not, after shutting off the water, you will need to repeat this procedure with the hot and/or cold stems also.