Cranks slow with the key, fast at the relay

Dana67,
You are missing the point. Without the screwdriver shorting out the relay contacts that energise the sol, the starter cranks slowly. The starter can only crank slowly, fast, or inbetween if the starter relay is energised. So the relay is operating but the internal contact points are likely pitted over years of use, from the high sol current. The pitting is causing a voltage drop from the high resistance of the contacts, which in turn reduces the current to the sol & it's ability to make pull in the sol armature disk that bridges the starter terminals. Bridging the relay contacts with the s'driver gives the sol a little more current, enough for the armature to pull in the armature disk more firmly & provide full current to the motor. The sol contacts are copper which wear away with usage & make poor/no contact. The dreaded 'click'. I build up the contacts with silver solder & that restores starter operation.