My question is about the effectiveness of stabilizer over a long
period of time.

My boat is normally stored from oct-nov to june-july. At the moment,
I have about 40 litres of 2 month old gazoline in the 100 litre tank.
Should I try to drain it and refill with stabilizer added to the gaz ?
Or should I just add fuel to fill the tank and assume that adding
stabilizer will properly treat all of the fuel for 8 months? The motor
is a 90hp Mercury 4-stroke.

AZ