Sumo, I've been through a half-dozen changes of Mobil 1 (5w-50) since the ticking started and recently moved to BP Visco 5000 (5W-40), and had no change.
nismoman18, got a url for this stuff?
Busky2k, an engine oil flush was what originally brought the ticking on. At first, it was only lightly ticking when cold, but its progressed to very loud ticking whether hot or cold. I guess whatever got dislodged during the flush travelled through the oil system and got stuck in the lifters. Your the second person to recommend trying 0w-30 weight oil, so I may give that a go.
The RB26 doesn't use hydraulic lifters but the RB25 definitely uses them, same as the RB20 (I think).