Hey GregZo,
reed switches are hermetically enclosed in glass cylinders so are dust-tight, not subject to corrosion and maintenance-free. However, unlike inductive proximity sensors (e.g. Omron E2B), it seems their life is not endless:
Life
The mechanical motion of the reeds is below the fatigue limit of the materials, so the reeds do not break due to fatigue. Wear and life are almost entirely dependent on the electrical load’s effect on the contacts along with the properties of the specific reed switch used. Contact surface wear occurs only when the switch contacts open or close. Because of this, manufacturers rate life in number of operations rather than hours or years. In general, higher voltages and higher currents cause faster wear and shorter life. Depending on the electrical load, life can be in the range of thousands of operations or billions of operations.
– Source: Reed switch – Wikipedia
Reed switches still have mechanical contacts, photoelectric sensors like on the Onefinity Elite Series or inductive proximity sensors not, so only the latter two have really infinite life.