My tub faucet is leaking from inside the diverter control arm inlet ( little whole below the valve with yellow arrow). Any idea if it can be fixed without replacing the whole unit? The red arrow points to the stem that controls both hot and cold water. I don't know the make and model as the trim plates markings have worn off. The lever that controles the shower head diverter just slides into the whole (yellow arrow) and controls the flow to the shower head by sliding to the left (off) or right(on) the blue arrow points to the diverter control lever on the trim plate. Don't know the make and model.
There are seals inside the diverter which can be replaced. This may be an O-ring or a more complicated seal. Turn off the water at the valves. Unscrew the diverter stem and take it to a homestore or better to a plumbing supply.