My fifth gear stalls and makes a lot of noise when I enter it but the 6th gear works just fine.

I drive a Mercedes-Benz E200 Classic (W210), the problem is when im driving and I go into the fifth gear the engine makes a loud noise like im in the wrong gear and sort of stalls but when I go to the sixth gear it moves just fine. I am worried because I dont want to destroy the engine or overwork it. Thank you