I've been wanting to give a shot at fitting zn standard seats or tried different models but haven't had the chance yet. Through all the web searches I've done, it doesn't appear right away that any other seat is interchangeable.
That doesn't mean that noone else has managed to do it, though, and didn't think to put the info out there for others
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My seat pan is a bit crusty as well. If someone could reproduce them in any material (plastic, fiberglass, aluminum etc.) for about 100-200 USD I would definitely be one of the first in line to purchase one!