Dripping connection

[johnwilky53]

We have had what I have now discovered a dripping mains to cistern connection ( heavy dripping ) in up stairs bathroom ,only discovered when we observed stains on the ceiling in the room below the bathroom. Is it possible how this could manifest the problem or would it be likely I have a more serious issue .Tricky diagnosis I know for info it's an old property ( but modern style plumbing ,,,10 years )

 

[Knappers]

If its screwed to a plastic thread then likely split and fill valve needs replacing.
A pic would help(Not sure I've understood completely)