Couple finishing questions

1) I have a can of General Finishes Arm-R-Seal (oil/varnish) that was 1/3rd full that filmed over on me. Is it okay to use the remaining finish or should I trash it? What symptoms should I look for in a test piece?
2) Is it okay to use the Arm-R-Seal over a shellac sealer coat? I've got an issue where I tried to use an oil based ebony stain on actual ebony because it had some ugly light brown spots in it. The stain covered the spots, but when I put on the Arm-R-Seal they came back somewhat. I'm not exactly sure what's happening there, but I'm guessing the stain is not penetrating and the finish is redissolving it making a translucent black finish. You can't see the spots under normal lighting, but under direct light they are quite noticeable. I would just do a shellac finish but it's a jewelry box destined for a teenage girl and I don't think it would hold up.
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