I have a three year old Colnago with Record parts. I recently replaced the cables, but the rear derailleur shifts very stiffly, almost hard to shift. Then it skips cogs when it shifts. I recently noticed the that shifter on the handlebar no longer clicks when I shift, like it used to do. Changing the cables made no difference. I have the original shifter and rear derailleur, and about 12-14K miles on it. Any suggestions?