Do you have any info on the manufacturer and model of the toilet ?
My Sealand 210 , has a return spring in the pedal pivot that broke at an inopportune time , giving the same issue.
A lot of manuals with parts lists are posted at this site: below: , or available at the manufacturers web site as free downloads.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.