stinky soft tissue on orchid sop. coccinnea

[Leafmite]

I would remove the bag and put it near a heating vent for a couple of days. Normally, I keep my plants away from heating vents but in this case, you want to keep the plant dry, warm, and disinfected.
I had this happen a few years ago and lost most of my cattleyas and a few other orchids. I discovered that it was caused by calcium deficiency. Now I add a little powdered milk to my water in the spring and summer growing seasons and keep eggshells in my medium. I haven't had any trouble since. This can sometimes run through a collection, too, so watch your other orchids.
Good luck! I have added these links to make it easy to gather further information.

Orchid Pests, Orchid Diseases
http://www.houstonorchidsociety.org/...ySueBottom.pdf