Fingerprint sensor - mystery internal part - suggestions welcome

I have a Huawei MediaPad M5 10.8 (there is no M5 in the device list) - recently tore it down to repair a number of parts. One issue was that the fingerprint sensor was being very temperamental. When I opened it up there was a substance between the front shell and the sensor sat on the motherboard. It was pink, thin, elastic, and had already started to crumble like old thermal paste. I have no idea what function it served apart from providing some kind of cushioning when pressed. My suspicion was that this degradation was what was causing the intermittent failure of the sensor. Unfortunately, now the substance has disintegrated completely and the sensor no longer works at all. So my question is, does anyone know what this substance is called and if I have to actually replace the entire sensor?