The corrosion related failure point on raw water cooled 1GM10's is the steel oil line that runs across the engine just below where the water pump mounts. Any drips from the pump shaft seal - and its very common to get grooving of the $%^*ing expensive shaft if you are in estuary water with any significant amount of suspended silt - land right on this steel line. Have a replacement line made up in copper and you can be pretty confident your engine wont dump all its oil in your bilge and promptly seize.
If in silty water, it is worth cutting a drip deflector from a sheet of fairly thin polythene and fitting it between the water pump mounting flange and the block. Replace all the pump mounting bolts with A4 or 316 stainless and put Duralac bichromate paste on all the threads and you will have no further trouble so long as you keep the pump's shaft drain holes reasonably clean. Otherwise the buildup of salt from a slow weep can eat away your aluminum timing case cover where the boss for the bottom pump bolt is.
The injection elbow is a wear part and should be checked with a bright torch and a mirror to look up it annually as a minimum. Also, to avoid corrosion it is best to remove both the exhaust and water hoses and seal it with a plastic bag and tape, preferably with a desiccant sachet for your winter layup. You should bag the intake as well, but thats' far less critical.
Failure to check the elbow results in undetected pinholing which results in exhaust manifold and exhaust valve corrosion. If it goes undetected for long, you will then need a new head at over £500 + misc parts and labour.
It is also a very good idea to leave the engine close to TDC on the compression stroke (when you hear the injector creak its right where you want it) so both valves are closed and you don't get rusting in the cylinder or on the valve seats due to condensation from the damp atmosphere produced by the waterlock muffler and the salts in the hoze if you aren't going to use the engine for the next month. Its dead easy to do, just decompess and crank very slowly, stopping when you hear the injector.
My 1GM10 is 25 years young and still going strong.