Help Please: Removed Cat Heat Sheild...What's This?
 

Hi guys. I was putting on my winter tires/rims this morning and decided to pull off a cat heat shield that's degraded and has been rattling for weeks now sounding like hell.

Anyway, when it was off I noticed this thing behind it. There's a little rubber cap hanging off of it. The cap was off when I noticed it so I put it back on assuming I had knocked it off while removing the heat shield. The square housing around the base is imprinted with "EPDM" and there was a small drop of some sort of fluid on the tip where the rubber cap covers. It's on the driver's side. I checked the passenger side and it doesn't look like there's one over there.

Anyone know what it is and whether the rubber cap should be on or off of it??

http://i66.tinypic.com/34sfksi.jpg

http://i66.tinypic.com/35d2kb8.jpg

Is the car a 6mt? This wouldn't be your clutch bleeder screw?

Yes, it's a manual. I was just over on the Zspeed website and they have almost the exact same picture on the listing for the HD CSC (which I just had installed a month ago).
Is there a difference if I leave the cap on or off?

Just leave the rubber cap on.

It's the same as the rubber caps that cover the break caliper bleeders.

It stops any debris or dirt from entering the hole.

Thanks guys! I just wanted to make sure I didn't accidentally disconnect something!