I've heard reports of scale damage from mineral oil that was just left to sit on snakes. If you use it, just use it to kill the mites on the snake then wash it off really well. Then before you put the snake back, scrub the cage out like it was a biohazard site. I successfully treated mites in a single snake using a similar method (I used MiteRX). If you have multiple snakes, using this method gets to be an uphill battle. Using a permethrin spray (Provent-a-Mite, Black Knight, Rid) is probably your best course in this instance.
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Peter: It's OK, I'll handle it. I read a book about something like this.
Brian: Are you sure it was a book? Are you sure it wasn't NOTHING?