1991 Passat GL Sometimes wont start

[drad2000]

I have a 91 passat and sometimes when I turn the key nothing happens except the lights. I believe it must be the Park/neutral safety switch because some times when I move the shifter from drive to park and such it sometimes starts. I was wondering if the sensor can become dirty and cause it not to work or if something can be tightened to make the sensor work. I really don't want to go to a vw dealership unless i have to.
Thanks,