Grohe 42181 toilet filler valve leaking?

Thanks for your responce. This is a real mind bender. The valve has a Polystyrene float which is screwed onto the valve body. It is adjusted so the water level is well below the overflow. On the top of the unit are two seals. One a diaphram and the other a small black seal that sits inside the valve lever. The repair kit came with both the diaphram seal and the small lever seal. I have replaced both. However it still leaks from the top valve area. Everything is tight. I suspect I may have to buy a new complete filler valve because I just can't stop the constant drip.