I've been working with Perkins engines for over 50 years and correctly maintained they'll see you under the sod first.
The 6354, along with its smaller 4 cylinder brother are considered the benchmark of diesel engines.
If a Perkins engines working parts become worn, cylinder liners, bearings etc are relatively easy to replace with rebuild kits from www.parts4engines.com
For all marinization parts for Perkins engine go to www.ejbowman.co.uk
who are the OE suppliers.
Boat engines rarely wear out, its the owners lack of TLC that causes the majority of problems.
If I may make so bold, most people service the engine at the start of the season which is absolutely wrong.
The engine produces tiny amounts of acid during the warm up period which is why its best to start your engine, check oil pressures are good and then place the engine under a light load until it reaches operating temperature, then you can run it hard, equally when you've finished a long hot run let the engine cool down at tick over speed for 7/8 minutes to dissipate any thermal stresses within the engine, this is particularly important for turbo charged versions.
To check if an engine oil is old, dab a little on your tongue and taste it, you will taste the acidity, now do the same with some new oil and you'll find it sweet its an old fashioned way, it won't kill you and it works.
At the end of the season change your engine oil, use flushing oil to clean the working parts, drain it and refill with the correct grade of oil, I use 15w40 series 3 (for turbocharged engines).
The working parts of your engine are now bathed in clean oil over the winter period ready for you to start cruising in the spring.
Update your records and write on the oil filter body the date of replacement.
It goes without saying that you would also change all the fuel filters at the same time.