Yes, the gum stuff.....Actually, it might be just that in this case.
But I'd rather not start with getting the engine out from the plane , without having replacement membranes ready.
Its a big job , and you dont want to risk doing it for nothing. (Well, its not that big, but I hate doing it, anyway.)
Another sentence that is a bit funny, in the manual;
First you read that the diagraphm in a petrol carburator is degraded by ......yes, you guessed it; By petrol.
And then this;
"Generally speaking, there are very few things that will keep today's modern gas engines from starting."
hehe.