The peroxide isn't to spendy. You can use it for quite a few skulls. I have 6 gallons of the stuff in varying stages of use. The old stuff I will sometime add to the degreaser on non antlered game skulls.
Make sure you get all the white deposits off of the skull before you whiten. I go over the skulls with a stiff tooth brush a couple time during the degreasing bath.
After the degreasing bath I'd have pulled the skull out and let it dry completely for at least a week to see if their is any more grease. It will bleed out and make the skull look wet in areas. If it does this back in the degreasr for another week. Here is a photo of the deer I shot this year. I took it out of the degreaser about 2 months ago and haven't had a chance to put it back in. You can see that the grease on the top of the head.

The elk I would let go for at least another 10 days in the degreaser.
One thing i will mention is you may want to wrap a couple strips of paper towel around the nose of the deer and wrap electrical tape to hold the bones in position while they dry.


You can also see the yellowing in the eye socket and bottom of skull. That is grease!