Generally reliable; however care must be taken to re-pack approximately every 3 years. Shaft wear and crevice corrosion can occur under the packing especially when worn packing is over compressed to stop shaft leaking. If flexibly mounted then the rubber hose should be replaced as a rule of thumb every 10 years. The flexible hose is an integral part of the craft as it cannot be closed in the event of failure. Heavy walled rubber hose with robust attachments should be used. Stern gland hose which has similar properties to exhaust hose (but without the wire reinforcement) should be used. The hose ends should be double clipped preferably with 316 stainless Mikalor type clamps. These seals should be tightened so the expel a drip of water every minute or so when underway. If a greaser is fitted then a turn at the end of the trip should reduce the water ingress. The disadvantage of this system is that the bilges always have water in them.
If the gland cannot be made to stop the water ingress to a drip every minute after new packing has been put in, then more than likely the shaft will be worn and possibly needs replacing. Other solutions can be increase/decrease the length of the flexible tube so the packing sits on an unworn part of the shaft or replace with a face seal.
Flexibly mounted oil lubricated lip seal. Seal below is a discontinued brand bin early 2000's by Halyard. No service parts are available for this item. Oil levels should be monitored in reservoirs. Replace with another system if losing oil at the seal.
Picture below shows a flexibly mounted water lubricated lip seal. Distributed by Tides marine. In current production.
This face seal is old and in outwardly poor condition requiring replacement. The shaft is misaligned to the stern tube. However on run up the seal was not leaking although there was evidence of previous leaks. Face seals rely on the integrity of the engine mounts. If the engine moves forward then the seal will open causing a large leak!
Deep sea Seal made by Manecraft. Face seals have a stationary seat attached to the stern tube and a rotating seal . It does not rely on contact with the shaft to achieve a water tight seal rather 2 faces that are pushed together with a compressed bellow. The above seal has had the emergency sealing clip tightened and is leaking heavily. (The craft should not be run up once this has been tightened).