funny oil problems

hi i have a f100aet 2002 four stroke and i had the problem of oil leaking out of the small hole below the exhaust manafold, also starting up it dumped heaps all over the water, striped down and found the water channnels blocked by sand and over heated the manafold and destroyed it basicly, replaced all the relevant gaskets and seals and of course the manafold and , no more leaks and running well at idle, went for a short run and overheat alarm on control box sounds at more the 1900 revs so returned to port, oil light on digital flashing , pulled the dipper and overflowing with milky oil. arrrhgh, i am thinking maybe sand also in water channels around head gasket so do i pull the head or any other advise please would help, i live in a very remote place so need some advise before i pull the head and have to order head gasket.
any help is greatly welcomed
regards
Ian C

[boats.net]

You need to take apart and inspect everything block, water passages for corrosion damage.