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