Assuming the inquiry if for the dripless seal on the 1999 450DA vee drive interior shaft.
If all correct, then that part should get immediate attention / probable replacement. Do not continue operation until this is resolved.
It may be that the dripless seal carrier is fine, just requiring replacement of the seal. If so, even though it is possible to implement that service while the boat is floating, even though I am at expert mechanic level, I would never undertake that service while floating if the option to perform while on the hard existed.
Always remember / perform the two essential periodic dripless seal tests. I do this annually on my boat. With the hose disconnected at the dripless seal and the hose barb capped off, ensure the running engines provide the specified raw water supply. With the engines off, the raw water hose disconnected from the dripless seal hose barb, ensure that unfettered raw water ingress into the engine compartment exists.
If the boat fails either of these essential tests then immediate correction is required.
