Quoted from Brich:

Finally found a source for the "twinkle" effect film on the Future Spa backglass!
Looks perfect when lights are in motion. Local dude helped me source a small roll, I will be cutting some sheets to size, anyone let me know if they need some, I can list some for sale in the marketplace as well for anyone else that is looking!

Quoted from NimblePin:

Most of the time the diffuser just falls off due to the age of the game and is either quietly sitting in the head, or the bottom cab, buried under old bulbs, rubber, coil dust, etc...
Clean it, double sided tape it and you're good to go for another 38 years.