Thanks for the comments.
The final bleach was mostly 40% peroxide from beauty salon, paint it on with a 1" brush and let it sit in sun. Wash it off a few days later and redo, leave skull in sun again. I confess I also used a bit of chlorox in a few places on the buffalo skull that were sort of yellowish, it did the trick. Chlorox is usually considered bad because it is too agressive and may cause some joints to become loose. But that damn skull was so thick I didn't think it would matter.
I usually clean skulls by boiling (after trimming) and pressure washing, but with the buffalo skull I first tried soaking in a garbage can (barely fit) for several weeks. It was stinking up the neighborhood so I took it out and blasted it with a pressure washer for about an hour, man that was a nasty job. Then I managed to find a pot (#2 washtub) big enough to boil it although it didn't entirely fit, had to rotate it around several times. Then I still had to blast it with the pressure washer again for another hour. There was all sorts of nooks and crannies with some stubborn grissle that took a lot of blasting to get loose. By far the toughest skull I've ever done, maybe I just should have paid the beetle guy.
Both skulls were sprayed with satin acrylic, which helps keep them clean, and give them a nice look, IMO.
JR