That is the Volvo
seal. Manufacturer recommended replacement is every 5 years. I met somebody who replaced it on haulout. He told me that after 18 years he thought it would be wiser to replace it although it still was not leaking.
It is essential to purge this seal after every haulout. This purging consists of eliminating the airpocket that is present after every haulout at the position of this seal. Because of the upward slope of the shaft. Not purging results in the outer seal not being water
lubricated and getting hot and wearing out. After that it is to late.
The Seal has 2 lips, the outer one is cooled and greased by seawater. The second safety
one cannot be greased by seawater and needs to be kept greased with a good marine
grease. My grease for this is blue.
The difficulty is to get the grease on the other side of the inner lip. Best way is to cut a (Mc Donalds or other) straw in half and fill it with grease.
Press the end a couple of mm under the inner lip and press the grease out of the straw in the space between the inner and outer lips. I do this once a year.I have somewhere a picture of a cut open Volvo seal. I will have to look for it.
Found it faster on the web.