Not sure if lubrication is the source of the problem, although it works wonders for slow sunroof mechanisms. You won't know until you actually inspect the assemblies.
I've used lithium grease when installing new assemblies in my 300E. Seems to work just fine.
Just don't go crazy...a little dab'l do ya. Too much and you will introduce a dirt magnet into the system.
I put a little on my finger tips and run it across the length of the cable. I even have the assembly attached to the power switch, so I can move the cable and lube everywhere. Just don't try to lube with your fingers WHILE operating the switch, or you will wind up with missing fingers like your old shop teacher in high school...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car