My reasoning is more based on the mudras that followed, as I noted in my previous post. Also, althought not completely relevant, I'd just like to point out that in the past, the incense offering prayer and mantra were exclusive to the evening service and the tea offering verse was used in the mornings, but there is now trend to do away with the tea offering verse. I would think that the mantra used in the Korean services is probably OM VAJRA DHUPE AH HUM. The influence of tantric Buddhism is everywhere in East Asia.
So Korean Buddhism has more esoteric practices than Chinese Buddhist liturgies, then? This is interesting. Do you have any resources (in English or Chinese) about Korean esoteric practices? I'd love to know more. Thanks!