Evap emissions system leak - where to now?

[blackmercedes]

My 98 C230 has, once again, a flashing low fuel light and CE light with P0442 and P0445. I've replaced the underhood valve (name escapes me now) and the shut off valve (in the wheel well) and both fuel level sensors, as well as adding a new fuel cap for good measure.

Where to now? I think I've run out of parts to throw at this stupid problem. At least the CE light was off for a while...