Before you loosen the set screw at least fasten a hose clamp in front of the collar so the collar can not slide forward. Most dirpless do leak a little when the shaft is turing, but when not turning should stop dripping.
There are two areas a drippless can/will leak, between the collar and the bellow/boot seal, and the O rings inside the collar. If between the collar and boot seal then slide the collar back wards for more pressure. If the O rings for a temp fix, they make Emergency Tape that stick to is self, weather oily/wet, that you could wrap around the shaft to form a seal, with a hose clamp push tight up against the E tape. You should have E tape on the boat as it comes in hand, just like duct tape If 0 rings you have to pull the shaft back ward tro get the collar off and should be done with the boat out of the water.