I had replaced mine some 5 years ago (it was 5 years old) and it now replacing again. Seems its lifespan is 5 years.The membrane on my cockpit chart plotter has rotted in the same way (UV damage I guess) - its currently covered with some waterproof clear tape. I may end up swapping over chart plotters I've got one at the nav station below decks.
If anyone knows a supplier of the trackpads or can salvage one I be pleased to hear from them.
I went into Raymarine's European Repair Centre in Fareham (UK) - they wouldn't even come down to reception to speak face to face. They told me (over the phone at the unmanned reception) that they can't get replacement rotary trackpads from their suppliers so my only option was to buy a new chart plotter. So much for after sales support