This is probably the best way to get the box open, plus there is a fix. Better than cutting the metal latch which you would have to reorder. Just remember to cut the vinyl nicely before drilling a hole, so you can glue it up again.

http://www.matthewsvolvosite.com/fix-a-stuck-glove-box-tutorial.html

As to the pressure at the dipstick, it's not a lot. What you want is a light vacuum. Someone used a finger from a latex glove. If the dipstick gives you the finger, you have positive pressure. If the finger looks to be drawing in, pull it off and have fun. Just make sure the glove doesn't get pulled into the dipstick hole!!!

Klaus
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My advice is free, so you got what you paid for...