The speedometer/odometer died on mine a ways back; tach death occurred shortly after that.
Research reveals my speedometer is electronic and has no cable. Your car is 4 yrs. newer than mine; I'd bet a buck yours is also electronic.
There are threads on replacing the small plastic gears inside the speedometer and others that indicate the problem can be more electronic in nature vs. mechanical.
There are posts on this forum that show a couple of speedo/tech repair shops in California and a guy in Austin, Tx. who is highly touted all over the web. I spoke via email with the Tx. guy - he didn't seem to be too high on fixing the tach.
I prefer one-stop shopping, so when I get around to fixing mine they will likely get to visit the Golden State.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"