Got an A/C question

I got a 08 subaru forester and I noticed that the a/c compressor was cycling on and off so I added some freon. Stopped the cycling for a little while. Anyway I looked at the fill valve and it seemed fine and then out of curiosity I looked at the valve on the high pressure side and saw it bubbling from where the core looks like it screws in. Is there a way that the "valve core" can be tightened up to stop the bubbling/leaking?

I hope that this makes sense.

Anyone got a link to the tool that fits on the valve?