Zig unit in Autosleeper Topaz?

A water tank gauge is fitted as part of the Zig unit in my 1994 Autosleeper Topaz. In order to read the guage you press a button next to the guage, which then lights up and gives a reading with a needle on a scale. As part of this unit there is also a resetting knob to set the guage accuracy. If I remove the Zig unit faceplate, the whole guage unit is housed in a plastic box which is secured to the faceplate with small circular circlips which lock onto thin plastic studs. How can I remove these to get inside the plastic box without damaging the plastic studs which look easily breakable? Does anyone have an idea what might be wrong the gauge? The fault to begin with was intermittent but now seems permanent.