In lieu of Vaseline, I have discovered Fluid Film works well. I began using that a couple years ago. Much more convenient in a spray can.
To the OP, take the starter and have it tested.
What is fluid film, do you have a link?
As an apprentice we used nothing but Vaseline on the large rotating contacts of drum controllers and batteries, its really cheap from the baby section in a tube or jar.
I never work on bike electrics without it handy, its really good to dip wires in it before crimping them, the joint will stay fresh for ages instead of corroding, especially in a wet area.
Im sure theres better stuff available, but we Guzzi owners are known for being cheap lol