Usually it's down to the slave cylinder, usually also happens when the weather is warmer too, we do a slave, line and fluid kit should you need a replacement...
We do the belts here - http://cougarstore.co.uk/index.php?main_page=product_info&products_id=77&zenid=1369af12b1f320c63adf43d50a7618a5
The belts should be changed at 5 years, 45k miles or at signs of wear/cracks, this is what we suggest...
The sump plug uses a crush washer, so it can only be used once, needs to be changed at every interval, it's just the crush washer that needs to be changed, not the plug...