TC reported MCH key not able to turn clockwise. Unable to open up cab. ~~~~~ TC reported MCH key not able to turn clo     #3651 Check and found MCH key slot was stiff but functional.Check no physical damage on the gear and key slot.Observed some dirt between the gear to key slot surface causing high friction when turning the key.Loosen the mounting bolts & clean up the dirt ,key turning movement smooth and function test ok. Done by Arthur Sam. 13/06/22