internal toilet overflow weeping-any help appreciated

ive got a newish apt and the toilet has a weep constantly coming down the back of the toilet,im guesssing this is the internal overflow.
can it be adjusted ie via lowering or raising the float mechanism or could it be a washer gone........
its awkward to get to cistern as the only thing you can see at the moment is the toilet itself as cistern is behind a tiled false wall with granite top on it.
looks very nice but a bugger to get to.
any help much appreciated.

can be the float valve not shutting fully.
can be the flush valve seal at the bottom not shutting/sealing fully

Usually the latter.
You will need a flush valve washer.
Access is always required to the cistern, a fact that homebuilders are stupidly all too happy to ignore