Pls check my website
On the right-side, you will see some PDF links.
Download the Beogram 4500 pdf, and inside, you will find complete instructions to repair the piston.
If you do not wish to do the work yourself, I am happy to do it for you - Pls contact me on how to remove the main PCB for shipping.
Menahem
Learn from the mistakes of others - you'll not live long enough to make them all yourself!