You can do it yourself if you are reasonably hands on. The most critical issue is does it start easily from cold. Worn rings or an air leak in the fuel system will require 5+ seconds of cranking. If it starts up in the first couple of seconds then it is probably good.
After it starts look at the exhaust. A blast of white smoke is ok, but should clear up after a minute or so. Then warm it up, put it in reverse at the dock with the lines tied tight and hold the rpms at about 1,000. Then open the oil filler cap and hold your hand over it. You might feel a little flow but strong pulses are another good indication of worn rings.
Then after it is nice an warm, look in the coolant filler cap for bubbles. That is a sure fire indication of head gasket troubles.
Then check all fluid levels after you shut down and look for leaks.
If all of these check out there is not much more an experienced mechanic or an oil analysis will tell you.
But most older Perkins in the 5,000 hour range will require some cranking to start, smoke for more than a minute and might blow by a little from the oil filler cap. These can likely run fine for several more thousand hours, particularly in Caribbean temps where starting shouldn't be that much of a problem.