Sounds to me like DeepFrz has covered all your bases...
This is a great suggestion... If you can find a mechanic that is willing to work with you, you have a perfect opportunity to learn about your power plant. The 4108 is about as basic as it gets, and a $100 investment in some basic tools will allow you to do everything not requiring a machine shop.
Do the dirty work yourself (pull the engine, clean and degrease, mount on an engine stand) Then get your mechanic to come in and help with the compression
and leak-down tests. While the injectors are out for the compression test, its a good time to have "pop-tested" to check for wear
and proper spray pattern.
After the top end is checked, more dirty work. Flip the engine over, and clean it all up inside. Pull the oil pump strainer and have your mech come back to help "plasti-guage" the rod and crank bearing clearances, plus offer some advice on the results...
Couple of additional suggestions... The 4-108 was (and still is) used in a lot of applications outside the marine environment
. Massey-Ferguson tractors, and power plant for over the road reefer trailers are just a couple of examples. Good source for mechanics and parts
at a generally lower rate.
Check your local diesel shops for farm equipment
and over the road trucks before checking with the "marine" sector. For example your oil pump is a #41314089 (the original was not manufactured by Perkins) and is available from RF Engine
for $180 vs $420 from a "marine" supplier... Same pump.
Same advice for having the injectors tested/rebuilt and any other internal engine parts
Here also is a link to the 4-108 shop manual
. Everything you ever needed to know about your iron genoa
and how to fix her. Great old beast (ran one for 25 years) Keep oil in her, don't over-rev and she will last you forever.