My answer is going to be biased by my love for this board. Bought mine secondhand in 2010 from someone frustrated with the learning curve that had it for less than two years, and never put it into everyday operation. Just recently experienced a single blue line in the display and, rather than wait for it to finally crater (might have taken years), I opted to install an LED replacement. Other than that, no other problems have arisen.
I mention this because this was the first time I ever had occasion to open the unit up and check out the guts, which gave me even more confidence after seeing how well manufactured it is. A quality piece of kit overall, which is why Tascam has had such a good reputation for several decades.
Think about this, there are literally tons of older analog and digital desks, not to mention highly prized ancillary gear, some upwards of forty years old and beyond, that somehow manage to be repaired and maintained for professional use. Compared to keeping a Neve alive, finding parts to repair a DM4800 should be relatively easy, and cost effective, especially considering what a new console with the same capabilities would cost. This all depends on what you use it for, of course, and how important it is to you.
I see you are in Australia, and not knowing where exactly I'm not sure this will help, but I found these guys in Victoria:
https://techshops.com.au/ Maybe they can at least point you in the right direction if not help you directly.
Lastly, if it was me, depending on price, I would pick up that other DM4800. After that, I would find someone who really knows about the repair of your board, and if it is cost effective, fix it and either sell it or keep it as a spare.
Bottom line, properly cared for, these boards have a lot of life left in them.
My fifty cents,
Jack