Intermittant Transmission Lock out at startup

[cwhtrains]

I have been having some intermittant trouble recently getting my 2000 ML320 transmission shift lever out of park. I have been using a pen to push down the release manually and move the shift lever out of park, then everything works fine. Sometimes it releases thereafter for a couple of days, sometimes not. Is there something I can look for to see if dirty or borken.

Clayton