Over heating

[Buli]

Hello - New to the forum. 

Purchased an 80 series 1Hz diesel 6 years ago 380,000km (now has 440.000km) on the clock - lm the 2nd owner.

lm far from mechanically minded - but know some basics (oil change , fit brake pads , fuel filter etc)

The vehicle runs well , it uses approximately 500ml to 1lt of oil every 5000km.

The car is fitted with a Engine Guard temperature gauge (it has been verified at operating correctly)  - it runs at around 80 degrees C.

When under load - small camper trailer - it will run at around 90c up over 100c.

l have done a bit of research over the years & have discovered it is a pretty common problem and took advice on how to deal with it including addressing the usual suspects - viscus fan , new radiator , removal of driving lights (restricting radiator) , thermostat , engine flush , bubbles in coolant etc.

lm nearing retirement age and have to make a decision if to do a rebuild (as l will be hitting the road with the camper trailer) 

l have two questions 

- Is it OK to run the engine at 90c to 100c degrees (my local mechanic owned a 1Hz for many years with the same problem & he said he did run it at that temperature all the time without issue. (I will note at this point which l was unaware the factory gauge on the dash board will not show the needle gauge in the red zone at around 100c)?

- After investing in a rebuild will the over heating be eliminated?

Any friendly advice most welcome.