1992 Town Car Transmission Selector

I can place my transmission selector in any mode (reverse, Drive, Overdrive and Neutral with no problem). When I put the lever in 1st it does not stay there. Does anyone know where the problem may be. This Town Car has 52,000 miles on it. Any help is appreciated. Thank you.

I can place my transmission selector in any mode (reverse, Drive, Overdrive and Neutral with no problem). When I put the lever in 1st it does not stay there. Does anyone know where the problem may be. This Town Car has 52,000 miles on it. Any help is appreciated. Thank you.
could possibly be the lincage adjustment on the side of the tranny.