80 Series Gearbox/Transfer Case oil levels

Yep, they are correct. It was a problem on the 40, 55 and 60 series cruisers, but not the 80 and subsequent series.

With the earlier H55F gearbox as used with the 60 series and 70 series of around that vintage it was quite possible for transfer case oil to pass to the gearbox. You could replace that seal which involved a fair bit of work and the leakage would start again not that long after, or you could fit a tube between the two filler plugs and the oil would just find it's own way back into the transfer case. I did this mod on two Cruisers I owned and no problems. I never tried it myself but I have been told that you could fit the seal that was used with the auto gearbox and because it had double sealing lips pointing in both directions it solved the problem. Personally I found the tube solution worked for me.
I believe that all the 80 series used the later H150F or H151F gearbox and a different design transfer case. Basically the same box with slightly different 1st and 2nd gear ratios.
With these gearboxes there are separate seals for the gearbox and transfer case and drain channels between the two housings so if either the gearbox or transfer case seal leaked the oil would wind up on the road or your carport. This being the case, yes, a tube between the two filler plugs would not work for this type.
Have a look at the ID plates that should be fitted to the firewall under the bonnet. One of them should tell you the transmission type along with diff models.

Cheers
Pop

Yep, I had one fitted to my 60 series but no need on my 80 series.

Cheers

Waste of time on either. Had one on my 75 and oil would transfer from my tc to the gearbox.
But the gearbox is lower than the tc
So basic physics meant the transfer tube did totally js
Periodically I would drain and refill