The most common point of failure in any level instrument is the seal. Exposure to process fluids and varying temperatures causes gaskets to degrade over time. Keeping a spare set of O-rings and flange gaskets on hand is essential for routine maintenance. If you notice leaking around the housing, it is almost always a seal issue.
Without more specific information about the Visiontek GL-11, it's challenging to provide a detailed list of spare parts. If you have more details about the model or what specific parts you're looking for, I might be able to offer more targeted advice. Visiontek Gl-11 Spare Parts