Hi Kyril,
I picked up my V8 by accident with 184,000km on it 3 years ago. Poor guy before me had been the victim of an incompetent local mechanic. The car was dirt cheap because the front suspension was shot, the timing cover was gushing oil, the transfer box howled and the engine was running on 6 cylinders. The main selling point was that the transmission had just had $8000 spent on a rebuild (and I bought it for just over half of that.) By the time the mechanics had piled silicone over the cam covers to "fix" the oil leaks and broken two coil earths in the process, the poor previous owner got sick of piling money into it. To be honest I piled a heap of cash into it myself but it's been quite trouble free for 100,000km and still drives like new.
Two of my mates with large families and tight budgets did it the proper way, and spent $10,000-$12,000 on much nicer examples with half the kms... they are the two I had used the shudder fix on after flushing the original transmission fluid several times. Only one tube each car. I did the first one, then mailed the second tube to the other owner with photos on how to do it himself - also successfully.
So only one tube, and yes straight into the T55 fill plug under the air filter.
Apart from the typical Japanese timing cover and cam cover seals shrinking with age every 10 years, the stupid serpentine belt tensioner set needing replacement every 150,000km and the phenomenally stupid plastic fuel pressure sensor housing design, the engine is delightful in every way and the whole package has been faultless. I've been light offroading, towed the family van around most of Vic and NSW and love the old bus now more than when I dragged its sorry ass home the first time.
The real problem is what you'd replace it with. My V8 will keep up with most sports cars at the traffic lights, is the best tow car I've owned, works as a people mover for adults and gets me 10.5L/100 average. (13-14 with the caravan). What else could I do that with ?
One "issue" from the financial side is the "semi-regular servicing": it seems the car was built to be endlessly refreshed and will last forever: every 150,000km they seem to need a front end rebuild and serpentine belt kit. The parts aren't too expensive from USA (stupid money locally) but there's so much time involved. I've done a remove and reinstall 3 times on an angle drive and can do one in 3 days now, but I shudder at the thought of ever doing one again. I have VIDA/DICE (clone) and do all my own work but would hate to be paying somebody like the last guy did.
I am planning on getting another 250,000km out of mine now - like you say it owes me nothing and the only rational reason to ditch it will be to pick up another bargain V8 with less wear.
All the best. Don't bail on the old girl yet.