Weird growth in tap spout

[Bobcatbrewing42]

I have been using a used Tru Keggerator for about 6 months. It is great but there is always something new to learn. I was getting a musty off-flavor for the first couple of ounces each time that I poured if it sat for a few hours. Then the beer started to spray out of the spout instead of pour. This morning there was a tube shaped extrusion coming out of one of the spouts. It is a mold colony shaped like a tube that was gradually filling in the opening.
I used a wire cleaner to get out what I could from both spouts and started to take the assembly apart, which is not so easy. There is either some trick to it or the threads have corroded. I don't know how many years old this is. (bought used by my kids as a gift)

What is the most aggressive cleaner that I can run though the system? I have some brewers cleaner that is Sodium Hydroxide based that rips through organic compounds (including skin). Would PBW be strong enough to eat mold? Others?

 

[govner1]

Clean it w/ BLC. If the spouts are mounted using a round knurled nut w/ small holes around it get a tap wrench and it will make it easier to remove. If it's really stuck you might need some WD-40.
I'd take everything apart and clean thoroughly w/ B-Brite, rinse well, & run StarSan throughout the system.

 

[PhinneyWoodBrews]

Beer residue in taps will inevitably invite wild bugs to grow. I'd recommend soaking the tap and lines in starsan or equivalent sanitizer to kill those uninvited guests.