I usually clean my ejector with CLP and a brush. Follow up with a good oil
Jokes aside, don't bother with cleaners. Run it hard, replace 'em when the time comes. A 99 seems to benefit from some two-stroke oil in the fuel (1oz per gallon) but that's mainly for the VP44, not the injectors. I did zero science on the subject, by my 00' sure did seem to run noticeable smoother with 1os per gallon of s2o.