My guess is the top hose, tighten the clamp.... Can you see any bubbling when it is running? It could be the seal around the cap, are the screws tight?
Best thing would be to clean it all up, dry it as best you can, then put a paper towel around the top hose at the base..... if it is leaking... well self explanatory. Repeat the procedure if leak appears lower.
Personally, I would just tighten everything up in the area, clean it up, see if it gets wet again.... looks like it's been that way for a while....