Pre mix or not pre mix

my malaguti is 18years old and runs lovely but I'm thinking of running pre mix itstead of the pump just becouse of the age and not wanting the pump to Ruin the engine if it suddenly fails what do you think? Wise? Dose any one know what amount of oil i should put in the tank? it's standard other than a Leo vince and appropriate rollers and correct jet for the race pipe

 

And if I do premix is it just a case of emptying the oil tank and premixing.can I leave the the oil pump and pipes connected ?

 

From what i have read the autolube is far better way of getting the oil in the engine any way so maybe "if it ain't broke don't fix it" is best any way