CEL shows EVAP Leaks, Intermittant Flashing Fuel Light in W210

[aspett]

I have an ongoing CEL light which reads both a P0442 and P0445 (Small and Large EVAP Emission Control Leak) as well as the reserve tank warning light flashes periodically. Would the Charcoal Canister Shut-off valve be the most likely source? If so, where is it located (2000 E320 Sedan) and how can I test? Any other suggestions (I've already replaced Gas Cap).
Thanks,
Alan

[mbdoc]

Shut-off valve in located in the upper section of the rear wheel opening behind plastic cover.. common failure..

The sensor also is a common failure..made into the tank sending unit.

[aspett]

Would you know the part # and is there a way to test without specific equipment? Would the shut-off valve be more likely than the sending unit?
Thanks