HELP! Lost 4th and 5th Gear!
 

I went to back into my parking spot this morning and I could not get my 190E 2.3 16V into reverse. It was very cold out, so I figured I would just pull around and pull into the spot. So I go to back out this afternoon and it goes into reverse fine, but when I got on the main road I went to shift into 4th and the shift would go into the position of 4th but it would slide left into 2nd. So I held the shift in the position of 4th and let the clutch out and it would respond like it was in second and once I let go of the shift knob, it slid back into 2nd. So I tried to then put it into 5th and the same thing happened, only this time it would fall into 3rd and there was no 4th or 5th gear! What the hell happened, and how do I fix this?

Sounds like the plastic shifter housing isn't allowing the linkage to engage the shift rods correctly.
OR the rubber grommets on the shift levers are worn out.

I popped off the boot and I have (visual) access to the plastic housing. What should I do now?

I drove the car onto some ramps today and got underneathe the car to look at the rods and the grommetts, they all appeared to be fine and operational (I had my brother get in and shift back and forth between gears). But when he put it into 4th the rod for 2nd and 3rd slid into 2nd and when he put it in 5th the 2nd and 3rd rod would slide into third. The 4th and 5th rod and linkage worked fine if I pushed them myself, but they did not move the shift lever. What should I do now?