MTU 183 heat exchanger

Check with a radiator repair place. Hopefully for you the ones in Aussie will be as skilled as the ones in NZ.
If they cant do it they might be able top point you to someone who deals with boilers and boiler repairs.

I had a bit of time so had a look. This lot look like they might be up to it. https://www.inter-marine.com.au/service/heat-exchangers/

Which MTU 183 version exactly? And which heat exchanger?
If it's the heat exchanger of the engine cooling circuit that you are referring to, I can't remember any version of MTU 183 whose HE isn't built with titanium plates interconnected with rubber seals, and I did hear of the latter needing replacement (after 20+ years).
AFAIK, those seals are still available from MTU, and their replacement demand a fair bit of patience, but other than that is no big deal.

I'm a bit surprised by your comment on corrosion though, because that's unheard of, in those HEs which as I said are made of titanium.
Or are you referring to the aftercooler, maybe?

Coming to think of it, I just checked my files related to a MTU 183 powered boat I was involved with about 7 years ago.
She had V12, TE92 version engines, and the attached pic shows a heat exchanger with one of the rubber seal I was referring to, and that had to be replaced. But as you can see, the titanium plates were as good as new (that HE was by then 25 years old, and the pic was taken right after removal, without any cleaning).

BTW, take this FWIW, but the best quote I had 7 years ago for those seals was $29 a piece, from these guys in Stuart (FL):
www.heatexchangerseals.com

U R welcome.
All the best for the job, and keep us updated about the result in due course!