Dometic 300 toilet foot pedal needs adjusting?

[Advtwindad]

Hello all,
I have a dometic 300 toilet that may need a flush pedal adjustment. It is a half push to fill and a full push to flush. Recently, the half push to fill has become impossible because the stopper opens with a half push and will no longer hold water, there is a slight space that the water runs through into the tank. Any ideas on how to repair this? It IS getting water and it IS flushing fine. Just can’t get it to hold the pre-use water.

Thanks!
Brian