Condensation does indeed cause problems and not just due to the HV. We have had it on the optics as well and it dont like it. As you have found out the optics have to stay clean and free from scrathces as well as this causes them to absorb power rather than transmit it, then they go bang. Done that a few times as well, takes ages to clean out the flight tubes and re-align the machine. Cutting assist air, air blowing through the nozzle, is a must as well. It helps to keep the lens clear of crap, cool it and blow away the cut material.