Resealing a mech shift 800 stringer lower unit

[THE BEEF]

I got problems, My lower unit is full of water, no gear lube.
I pulled it out yesterday from the dock and checked it.
After I pull the lower, do I have to pull the guts out of the unit or can I replace the seals with out total disassemably.I think I know why this happend.
I had a no brainer.
Beef