Yoshi really is such a beautiful Uro!
Them gaping their mouths generally has one of two purposes, panting to release heat (Mosca does this when he is too lazy to move from his hot basking spot), or if they are about to bite you. However if they aren't doing the other aggressive behaviours, like the "S" dance they are probably just panting. At least this is my understanding of this behaviour.
Hopefully Debb, Eve, or one of the other really knowledgable people will weigh in on the liquid secretion. My guess would be one of 2 things. Either it is just Yoshi getting rid of the "snalt" in his system and you happen to be catching it in liquid form, or it is the beginning of a respiratory problem. One of these would be normal, and one of them IS a reason to be concerned, that is why hopefully Lindsay or a mega-uro keeper will reply to you
. Until then, make sure that your tank temps are hot enough, and just watch him for any other trouble signs. 
Elizabeth
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1.0 Mali Uro Archimedes (May he rest in peace)
0.0.1 Egyptian Uro Zuberi Mosca Khu (Mosca)
0.0 Fish
0.1 Sulcata Minnie
1.1 Iguanas Flik and Loki
0.1 Newfoundland Jasmine (RIP)
0.1 Feline Winter
Indiana & Wisconsin