Hi
Old motors die normally because they are not used enough, an outboards needs to run regularly.
When the motor is in good condition there is no problem to run it on WOT.
Problems are normally oxidation, bad maintenance, carbon buildup ( the medicines are WOT or Evinrude Engine Tuner Spray ), overheating due to oxidation or a failing waterpump.
You have to be very careful with the VRO-Pump I recommend You to mix 2 % of oil with the fuel without using the automatic mixer of the motor.
Many motors died due to failing oil.
Regards