Suspected leak to the waste pipe of the WC with visible water at the base of the horizontal waste pipe. However all the plumbing/services are concealed within a 1.2metre high stud-service wall. Could the leak be repaired/accessed without taking the stud wall down?
Difficult to advise, however the best advice is to check at the highest visible level with a tap running and work your way down. If there are no leaks from visible joins then yes there will need to be access through the wall. Just check for runs in the manner described