What to do for circumnavigation?

[myocean]

We have a cat from 1999 with Volvo motors. Thay have about 4000h or so (the displays are not working anymore).
I have a technical background but not with lots of mechanic. However, I could get some training.
So what to do with those motors? When asking 'experts' some say for a circumnavivation new motors are highly recommended. The old machines are just nor reliable. Others (the more mechanically oriented people) shake the head, saying that 1999 is really not old. What should be the problem with them, they ask.
So what would be the real life difference for me?
Certainly we would do a complete check before starting and exchange some critical parts.
Would I (probably) have more maintenance work to do with the old motors? Is it realistic to solve all problems even in the remotest places?

[atoll]

if they are volvo 2003t engines,they were only designed for 3800 hours!

[micah719]

Run them in reverse for 201 hours, then replace them under warranty.

[POH]

My recommendation is get them serviced by an quality mechanic and listen to his advice.

You can also get oil analysis done on them to have a view on them from the inside - will also help you decide on new vs tuning vs recondition etc.