Yes it's probably the most common problem of how most Victa's die. They really needed to put a sticker or some type of moulded lettering around the fuel cap area saying "2 Stroke Fuel only" just like most diesel vehicles have "Diesel Only" on the fuel flap. I know dimwits still put 91 Fuel into diesels but probably not as many if there was no blatant warning at all.
I'd say that the engine which was originally fitted ran about two or more tanks worth through it so as to get like that.
Cheers,
BB and Victa every now and again, but very seldom.