Should I re-build my engine?

12 months ago, I bought a 1999 Mitsubishi Delica with a 4m40 2.8TD engine (diesel).

• The vehicle itself has done 120,000 miles and runs very well.
• There is a very slight oil leak somewhere.
• There is no service history with the vehicle.

I bought the vehicle as I am looking at converting it into a campervan and going on a round-the-world adventure starting sometime next year.
I recently acquired a fully stocked workshop/car garage for the next four months to concentrate on the conversion.

Mechanics:

• As I now have space, time, tools and physical help,
  is it wise/beneficial to pull the engine out and give it a complete
  overhaul?
• If no overhaul is required, what would be your main concerns?

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I have always done my own repairs and I can confidently say I can do the job, my main reason to ask is wondering is it really worth it?

My main worry would be any issues while on the road. Also, the timing chain as far as I am aware of has never been changed.

Thank you