I don't find my 1998 C230's pedal pressure uncomfortable, but I have been driving MB's for some years, and may be used to the longer travel and higher pressure.
A 1999 car might still have warranty coverage, and you could ask the dealer to examine it. A better bet is to find another C230K (99 or 00) and compare it to yours. Maybe look for one for sale.
The car uses a drive-by-wire system that has the throttle cable ending at the second firewall, connecting to the engine via electronics. There is a spring return system at the final point of the cable, and it is quite accessible at the drivers side near the fusebox. You should have a look and see if something is binding, but I would be wary of applying any type of lubricant, as there are lots of electronic components in this area...
1998 C230 "Black Betty"