The Lignum Vitae stern tube arrangement has now long since been taken over by an oil filled stern tube.
The arrangement is a stern seal, which usually consists of a pack of lip seals of two facing inwards to keep the oil in and three facing outwards to keep the water out on the outside of the vessel and then another lip seal on the inboard side of a couple more seals. Between this is an oil filled stern tube with a lubrication system and a white metal bearing arrangement. If there is an external "P" bracket or a "A" bracket this could well have it's own pair of seals. oils system and more white metal bearings.
Alternative seal arrangements could be a face type seal and even some of the more sophisticated ones have an inflatable tyre incorporated into them to enable components of the seal to be changed with the vessel in service.
As you can imagine this is prone to leakages and many a ship has had fitted lower oil system header tanks in an attempt to slow down the loss of oil from a leaking seal. There is even a special oil produced by Vickers called Hydrox which is designed to allow water to leak in and emulsify the oil which with maintain it's lubricating properties up to about an 80% water content.
The traditional oil filled stern tube is still very common however, as with so many things the circle is coming round again and we are returning to a "stave" type of bearing. The differrence is nowadays though that the staves are made of a plastic material and incorporated into a backing so they can be slid in and out as two pieces. The significant differrence though is the fact that these are water cooled and lubricated so sea water is simply pumped through the bearing from dedicated pumps in board and there is therefore only a requirement for a single seal arrangement on the inboard side. "A" bracket and "P" Brackets are fitted with similar bearings and also water supplied down through channels inside the castings which do not require a seal and simply allow the sea water to escape to the environment.
This type of stern tube arrangement is becoming very popular as the environmental concerns are removed completely. Also the plastic materials are proving to be very resilient and lasting extreemly well with very little wear down over many years.
This is a popular manufacturer with cruise ships and a typical arrangement:
http://www.thordonbearings.com/markets/marine/merchant/compac.html