1991 240 Auto 142k miles.

Every morning or at least 8 hours of sitting, I start the car and cannot get the shifter button to depress. After sitting in the car and depressing the brake always first, about 3-5 mins pass then when I press brake I can hear the little cliking in the shifter handle that tells me that the button can be depressed and I can select drive or reverse. After this happend for the day it will allow proper operation at anytime. Is this the nutral swich going out? No one thing I do allows me to depress the button it just starts working after a few minutes. But, If I get into the car and just let it idle for minutes on end it still will not work till I start trying to depress the button.

Please Help, Thanks you very much ahead of time.