Electric Starter for 20 HP Johnson 1969

[John Drew98]

I had an electric starter put on my 1969 Johnson 20 Hp. The country mechanic had died and his teenage son took over. He put a Auto-Lite MDO-4002m12V starter on it. It breaks the woodruff key (half moon) I have replaced 3. It is not froze up I started it and ran for a few seconds in a water tank. The gas line was bad. Tried again and the new key broke. I used two OEM keys the last was one from Lowes.I think the starter is too powerful. Is that starter too powerful for a 20hp, Where can I get a starter which will match the 20hp? .