Navman 8120 chart plotter

[mrpelikan]

First forum post, so bear with me. Against my normal judgement on not getting involved in consumer electronics, I've been talked into repairing a boatie relative's Navman 8120 chart plotter. It turns out the issue is a dead inverter for cold cathode backlight. An LED upgrade is available from a vendor in the US but we need to decide whether to spend that many dollars on an older device.
That aside, on lifting out the LCD screen to withdraw the cold cathode I must have slightly lifted the protective glass front from the LCD screen.     Between the glass & LCD screen is a viscous (water-clear?) filler. This is probably to exclude the marine environment from LCD panel.
The filler has retreated away slightly from inner edges of LCD panel on 3 sides plus a couple of small bubbles under the glass. Due to the dead CCFL I haven't powered up the plotter yet but assume the bubbles and retreated filler will affect/distort the image.
Anyone know what this filler compound might be? Better yet, what could be used to fill the voids?