http://www.depcopump.com/datasheets/...10-24218-1.pdf
This pump has been overhauled twice and apart from that it has been
serviced with new seals but it keeps developing a leak. Last time (2
months after overhaul) the seawater crept through 2 seals into the
engine block. I had to take out 2 gallons of salt water. Now it starts
again to drip. since that last servicing I have only been in clear
seawater.

First of all, make sure that seawater can leak out from between the two seals;
there should be an unblocked outlet to the outside to:
1. prevent water from ever reaching the second seal.
2. clearly show that the first seal is leaking.

Secondly other new seals without survey, are unlikely to last. Look for:
1. rough/damaged surfaces where the seals touch.
2. a loose pump.
3. mis-alignment of the engine and pump axle, or a bent axle.
4. worn axle-bearings allowing to much radial movement for the seals to cope
with.
5. too much pressure on the cooling system due to (partial) blockage blowing
the seals.

Have a nice search (it's freezing here right now!)

Mees de Roo