The gas pedal on the 300se that I have in the stable is so heavy that I have thought of some modifications on the K-opening beneath the air-filter. The modification I was thinking of is to replace the cable mechanism with ball-bearings.

Has anyone done this?

Lubricate everything that moves. If it is a cable, you can get a device at a motorcycle shop that allows you to spray lubricant down the cable too. Just don't go crazy with it, as you know where the other end of the cable resides.

Pedals on all three of MB's that I've had were so stiff that the first thing I did to them was to remove coil spring about 6" long from mechanism down low on engine side of firewall. Drove 80 240D 185kmi without it; the 91 W126 has been without it for 65kmi; the 81 W123 has been without it for 12kmi. Pedals still have plenty of resistance; 'have never had a prob. with "throttle" return; they're just not so stiff that I have to work right leg so hard all the time holding the pedals where I want them. Pedal sure feels better to me not so stiff!!