Chris, The rubber needs to be only long enough to provide watertight joints at both the stern tube and the gland ends. The position of the stern gland is dictated by the length of the rubber and needs to well clear of the gearbox coupling. By “broken through” I meant that, when slackening or tightening the gland nut and its lock nut, it is relatively easy to apply a twisting force (torque) to the rubber tube. If the jubilee clips were not sufficiently tight, that torque could have broken the watertight grip of the rubber on either the gland or the stern tube. I assume that you have checked that the rubber itself is not damaged? There will inevitably be grease everywhere since you are injecting it under pressure from the greaser!