I have 3 of the 600 ex rt speedlites. last night as I was gearing up one of the units the adjustment wheel became really stuck almost impossible to move I had to jam my fingernails into the grooves to rotate it.
the other 2 units units seemed stiffer than usual. I took them to Canon service in Irvine 53 miles away,
the intake receptionist took the bad one back to repair and came back said it was normal. Well that made my day, I told the girl to try the other unit. duh...
A speedlite you can't adjust is useless. I think the lube used is gumming up the wheel as it was really cold here and maybe the heat from the flashing degraded the lube. either way its a problem especially for a $550 speedlite. My other two units are exhibiting bad behavior as well.. I really think the cold weather is affecting them..