Well set 3 seems ok so far as far as tint goes, although there is a dead white pixel near the top middle which I can just about see from my normal viewing position. Also when taking the plastic off the back I could clearly see that there is a gap between the panel and the electronics casing. On further investigation the top of the screen is bent backwards by about 10mm.
On both previous screens the yellowing was not the only issue - the first had vertical bands near black, and the second a vertical line visible on lighter backgrounds, including football pitches.
I have a 910 from last year which I passed on to my old man which has a yellow tint on the right hand side of the screen and I can assure you after a years worth of 10 hours/day on time on average, the yellow tint is the same as the moment I switched it on.
I am well aware that oled sets are not perfect, but for the money I paid I don't see how I should put up with issues that my previous plasma never had. OK the black level on it was poor compared to the OLED sets, but it could display a completely tint-free white screen, and there was no banding watching football.
I am going to check it on the football later and then watch a film tonight. If there's no obvious banding then I will overlook the dead pixel and bent screen, otherwise it's going back (for a refund this time I think).