Thanks for the info guys. Yeah, I've always heard (from factory Lexus mechanic buddies of mine) that the 1UZ-FE and 3UZ-FE are very solid motors all around.
Jacek, sorry for my bad wording, what I meant is that all the oil changes consisted of OEM Lexus oil and OEM Lexus Oil Filters (whatever they normally use). The GS has had regularly scheduled oil changes since day one.
I ordered both a PureOne and Royal Purple Extended Life filter for the GS430 so I'll flip a coin when I do the oil change.
The PureOne part number that came up for me was PL10241. I think the PL20195 might be for the 2JZ-GE motor (3L I6) in the GS300 (also the SC300)
I'd also be interested in seeing the UOA too so I may just do what John suggested.