They are mot 'sealed for life': they are 'sealed for death'. if you don't change the fluid, they WILL die. If you do change the fluid they can last for a very long time indeed. I don't know what box is in the latest Landcruisers, but the 80 & 100/120 series used the same box (along with a number of other manufacturers) and how often do you hear of Landcruiser gearboxes blowing up?
I've used the Gibbons method before, and I think it is the best. The FCP method will probably do the same trick if you repeat it often enough, but I suspect that you will use rather more fluid. The Gibbons isn't as hard as it sounds.
As for the fluid, that makes me nervous. You go into an auto parts store and they tell you that this that or the other is suitable. Bah humbug! Aisin don't make the fluids, oil companies do that. Esso/Mobil, and I understand Shell made the original fluid, and the specifications can be found online. JW(S)3309 is the correct spec, the Shell Spirax S5 (I'm pretty sure it was S5) is the same specification. (I think the (S) is the synthetic equivalent).
The way to make a decision on what to use is to read and make sure the specification is the same as (or so close to that it doesn't matter) that original spec whatever the fluid is. And if in doubt don't assume, ring the oil company and speak with their technical advisors.
I just sold a 2005 XC70 D5 with 402,000 on the clock, and the gearbox was changing better than the 2015 D5 I just bought. My mechanic mate is about to change the fluid in it (at 220,000, and I'll bet London to a brick that it hasn't ever been done - the previous [original] owner hadn't even changed the bloody cambelt - some people are plain stupid). He uses Total oils & fluids which I have looked at the specs of and it is very close to the JWS3324 spec which this box calls for.
Bottom line: if the spec isn't very close, don't touch it.
