Modern Vespa

I had a problem a while ago with the LX.

The engine "stuttered" a couple of times and then decided to not work at all.
After checking is saw that the spark plug cap was loose.

I tried to refit it but after a while it came loose again.
Now i find out that the spark plug and cap are worn out and don't fit properly to each other. There is no "click" anymore when you push to cap on to the spark plug. The sparkplug contact is visibly "worn out".

Anybody had this same problem? The LX has 29000 km (+-18000 mls).

I have the Malossi kit on the bike. Maybe vibrations are the cause of the problem?

Is there any corrosion inside the cap? I've seen the little spring clip that holds the end of the spark plug get rusty and break apart. I imagine that it could possibly break without corrosion, too. Good thing is, a spark plug cap is a cheap, easy fix!