"Liquify" is slang for spilling some liquid, i.e coffee, down into the shift mechanism. You could try gently removing trim piece and see if there is any evidence of this.

FastLane is a parts seller and one of the sponsors of this site. Link is at the top of the page, just enter your car and take a look.

I changed my bushings recently and the fault was purely mechanical. The missing bushings causing a slight misalignment, making moving the shifter difficult.

If you just can't toggle the shifter to show 4th gear, then it sounds more like a problem with the shifter itself.

glenmore
1991 300CE
2000 C280