i have been told i need to replace the bottom entry ball valve?

Try B&Q for a fluidmaster cistern kit but check with them it will be a suitable replacement.
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It might sound a bit stupid but take a digi picture of the existing preferably after flushing so water doesn't reflect flash, either print out picture or take camera with you to show then if they give a blank look the leave and go to plumbing store.

B
December 2010