On Monday, when I opened the garage door, I noticed a petrolly smell....and there was a suspicious pool underneath the bike. I found that my fuel tap was leaking.
The tank is easy to remove from a Spada, just release the seat, and undo the one bolt uncovered at the tail of the tank. Pull the fuel and vacuum lines off the carburettor, slide the tank back, and it's off.
The joint between the tap and the tank was leaking.
Two bolts hold the tap to the tank....luckily the tank was only a third full, so I could stand it on its nose to remove the tap. The seal for the joint is an o-ring which fits around the filter block. The ring was flattened and brittle.
A visit to an engineering supplier with the old ring secured a suitable replacement. It was soon installed, and the tank went back on the bike.
Result.....no more leak.