Ignition Saftey Switch

[JMan300sd]

Hows it goin guys. Im new on this board, aswell as fairly new at being a mercedes engine enthusiast. I take pride in fixing whatever is within my own ability and that is why Im asking from the experience of others. I have a 82' 300 sd that I love to death but for as long as Ive had it, its given me a problem with the park/neutral saftey switch. Often times after its been on a long drive it wont start in park and I have to move the shifter back and forth from park to neutral until it starts. I have a feeling that it might just require some contact cleaning, but I have no idea where its located. If it is a part that I need to replace, is there any place you guys suggest to order from? Can this defect be caused or lead to any other problems on the car? Thanks a lot guys, I really appreciate it