I would say that if you left the lorry parked up for 6 weeks, you could expect that the pressure would have dropped alright and the buzzer would sound as soon as you turn the key to the "acc" position. Small leakage is not a problem but if the buzzer is sounding every morning then you have a more serious leak. A lot of the air-lines are plastic and they are susceptible to damage - a good example being if anyone does any welding on or near the body or chassis, weld spatter could land on an air-line and melt the plastic causing a leak.
JD, May 2008