that is a hot topic of debate, i have a 94 merc and still use the injection system. i feel i am on borrowed time,but i love the convienence. the motor just runs better . i do inspect my hoses and make sure my pump is pumping the correct amount about once a year, but i also carry a spare gallon of oil and at the first hint of trouble, i dump it in the gas tank. the problem with that is sometimes the first hint is when the motor seizes.
if you have ANY doubts, i'd premix...