No, EvilV, you're not going senile :-)
I haven't got a Merc, but I've been looking for mudguards for a 305, & a 406 wheel, for my recumbent which I'm riding regularly again now. I remembered you posting some good prices for Merc's tyres, etc., so thought they'd have mudguards listed.
Have you by chance got a picture of them, to give me an idea if they'd fit please?