I've got one of these - my Dad bought it from new 30+ years ago, so that's why I'm trying to keep it running.
I had the front tank plate off to have a look at the fuel line and used gasket maker when I put it back together. My dodgy fuel line fix seems to be working so far!
The gasket was stuck to one piece and in good condition so I left it there and applied the gasket maker to that. I put fresh fuel in it this morning and now the only leak is from the filler cap. So I guess that might work for you.
I didn't find any gaskets for sale online for this. The guy at the auto shop is a mechanic on race cars - he said they have them in bits so often that they don't bother with gaskets and just use the goo instead (even with heads).
BTW does anyone know the carb adjustment settings for the 015L?