Well, I'm here and you're there so this is only my guess. I still say check the lifters. Listen to the youtube video post #7 in the pajero club victoria post you linked in your first post. It turned out to be a lifter and sounds pretty familiar.
On another guess, pull your dipstick and smell the oil. Does it smell like gasoline? If something failed and you ended up getting fuel into the oil pan (open injector, etc.) then the lifters wouldn't pump up, and oil pressure would certainly not be happy.
I really wonder if you are also hearing detonation (heavy spark knock) along with noisy lifters. I don't have a 3.8L engine, so I'm cautious to say, but there's a fair amount of noises going on there. Exhaust leak?, A/C compressor clutch wobbly?, fuel injectors seem really noisy to me, but listening again, much more probability for lifters, as the tick is fairly light in my opinion.
Where are you on the maintenance list? If a timing belt is in your future, then tackle it, and eliminate the hydraulic tensioner etc. as an issue. If spark plugs are on the list, then you have an excuse to pull the rockers and inspect and bleed the lifters.
Right now, I'm thinking oil change with correct oil and filter, then see about getting the lifters pumped back up. There is a procedure basically slow and steady rpm raise to ~ 3,000 about 10-15 secs per cycle up to 3K, then drop back to idle. Usually 10 or so cycles will do it. Obviously if there is trouble with the timing belt and/or adjuster then fix that first or risk piston to valve contact when it fails.
Anybody else with a 3.8L hear anything different or unusual with the videos?