My rear LED turn signal has gone out and I have no idea where to buy replacement parts and how to even replace them. Just to clarify i have a pre-facelift c300 with the LED turn signals.

 

Have you considered upgrading to facelift rear taillights as are in the 2011+. You can replace both taillights for about $233.(Depots). These have the light bar taillights and LED turn signals and look identical to OEM. Recent threads here about these.

 

I've read about those, but if I can save some money and just change the turn signal that would be better. Do you think id have to replace the whole light assembly itself?

 

I replaced mine with the Depots and have the originals I will sell to you cheap if you want to go that route. My car is '09 350 Sport with LED taillights. PM me if interested and we can discuss the price and shipping.