For The Love Of Port

Is there a hard and fast rule on fluid level (neck, shoulder, etc) for a super vintage bottle? In your experiences, how does it impact price and better yet, taste of the madeira? Madeira could withstand a little extra oxygen in the neck, but I'm assuming it's the bacteria and mold's that might slip in due to a bad cork, etc?

Thanks for your advice in advance!

...also, how does re-corking and re-waxing effect value? It would seem from many of the posts that this can actually help? Thanks!