Ignition tumbler or something else?

[otto huber]

The car is a 1981 300SD. About a month ago the ignition key seemed to have one less click and feel easier to turn. At that time, the headlight warning buzzer would remain on with the headlights off when the key was in the ignition. I figure that a switch got worn out. Today a mechanic parked the vehicle and turned the car off with the steering wheel perfectly straight. We couldn't get the key to turn after several tries until we added some WD-40 and it still took a couple of minutes. Can this problem be remedied with a new tumbler and key, or is the problem with the locking pin?

BTW, I always turn the wheel 45 degrees before I turn off the car to avoid having the steering wheel lock up, but sometimes I forget and don't want to be stranded if I forget again.

Thanks