Great charity shop find a 1963 "Lambretta Serviceman's Book".
I had one of these back in the day and well remember trying to sort out my LI series 1 150 with the aid of the Serviceman's Book, a plug spanner, adjustable wrench and Phillips screwdriver.
After a while I got quite proficient, being able to drop the engine, change piston rings and substitute the original carb for a "Del Auto".
All the annoying bits about owning a Scooter came flooding back.
The fouled up spark plugs, the clutch/throttle cables that kept breaking.
The Manual advises owners to be prepared to live with noises and vibrations and "give up worrying.To prove it, swop machines with a friend for a few miles; both of you should find the other's Lambretta apparently sweeter running than his own."