What toilet part do I need?

My toilet still flushes fine but when you press on the pedal you have to put your toe under it and pull it back up. I'm guessing it's a spring in the water valve assembly -- should I just get the appropriate valve assembly kit? There's no leaking. It's been like this for over a year. Doesn't feel sticky, feels like a spring is missing or worn out. Actually I have a vague recollection of something making a sound at the time it first lost its ability to spring right back. Haven't changed that valve assembly for a very long time. Do I need a new pedal with that or will the old pedal work fine with a new valve assembly? I just tried some WD40 and now it's a little worse...phff.

Actually, now I'm thinking it's the spring cartridge assembly. ?


Thanks much...selling my rig after 15 years and moving into my first house. It's time. Appreciate all the help over the years...