Sub fail, no sound, but harsh excursion at power on.

Hello n Thank you. My friend brought me his Canton AS22 sub, because “You know how to fix stuff". Not really. I'm just willing to try.

No sound from this wired sub, but the outputs (or pass thru) to right +left speakers sound normal (pass thru works with power off too).

Fuses ok (2 internal, 1 external).

I notice that the sub has a large unpleasant excursion at power up - and returns; otherwise nothing: no buzz, no hum, no scratch, no noise, no vibrations. Cone travels well by hand, no rubbing. Foam good.

I opened the hood. Caps look normal, but (see photos) there is a hardened liquid spilled across one board. My first thought is sloppy glue, it is hard and brittle. But maybe not, maybe one small cap has “expressed it's opinion of music choices”, all over the board.

Please look and identify the mess.

Thank you, you electro-mechanical wizards.

Umm…I'm looking where to add photos…