Dudley cistern overflowing?

[rsk289]

I have a Dudley concealed cistern with electroflo flush, and internal overflow. There seems to be a very slight leak into the bowl, not much - if I wipe the surface clean, a drop forms and runs down into the bowl after a few seconds. It's not much but it's building up a stain on the porcelain, so I'm assuming I have an overflow leak. But - the water level is not overly high in the cistern, and I can't see any drops coming from the filler valve. I guessed that the overflow is the white 'tube' cast into the body of the cistern - if so, the water level's nowhere near the top of that.
Is there a problem here, or is this normal?
Then there's the intermittent failure to 'long flush' by the electroflo...

Thanks,
Roger

 

[PlumbBobBob]

most likely the seal on the flush valve is letting by slightly

 

[macackau]

Can you remove the flush valve to clean off any limescale and grit?