E420 P0455

[PBH]

I've had numerous issues with my 1997 E420 (90,000 miles). I recently replaced the intake manifold (drivers side was leaking) and replaced the catilytic converter on the passenger side (plugged, likely from the intake leak leaning out half my engine and making the other half too rich?).

I'm down to one nagging and apparently common problem: P0455 large evap leak.

I get all the common faults (the check engine light is always on and sometimes I get the flashing low fuel light when I'm stopped at a traffic light). The car sees to run fine but I would like to fix this last annoying glitch.

It is not my gas cap, so I'm assuming that the charcoal cannister or the purge valve is the problem, or possibly a failed vacuum line in the purge system?

So, finally, my question: Can someone offer some sugestions how to narrow down the problem? And, where are the charcoal canister and purge valve located? I'm leaning towards just buying a purge valve and swapping it out. I ahve used the search button to get this far, but I do not know what the purge valve looks like, or even where they are typically mounted.

P.S. I'm an experienced mechanic but a Mercedes imibicile as of today.

Thanks in advance for any help.