Okay, I think I may have this now.
The vent solenoid is under the seat and that is the one I should clean.
Does this mean the purge solenoid is the one by the right rear wheel and is it cleanable too?
Thanks a ton for your patience!

You're getting closer. The only thing that you will find under the seat is the battery, some wires, and some fuses. The vent solenoid is underneath the car. If there was an axle that went from one side of the car in the back, that'* about where it would be. Thats the one that you want to clean. The purge solenoid is under the hood. That has been known to cause some problems too but, let'* worry about that later.

EVAP canister purge valve (I think) Located above the front valve cover.

My 2001 SSEI had the same gas cap issue and it was the Purge Canister Solenoid.

Thanks for the picture, Mac...that is the purge solenoid, as you suspected. Jayman, you'll find that above the rear rocker cover on yours, right back where the injector sight shield attaches. You'll have to remove that to see it.

Yes Archon - I did mean underneath the car. Do I have to pay any attention to the one by the right rear wheel and what is it called then?
Thanks for the pic MACDRIVE that is awesome - I sure can tell where the saying comes from "a picture is worth a thousand words"
My ISP is acting up and I have a full day today but I will get at this and report back.

The one by the wheel is the VENT solenoid...the one we've been talking about. The one that MacDrive pictured is the PURGE solenoid. Different parts that do different things. If you prefer to start with the purge solenoid, as it'* easier to get to, we can. The only surefire way to tell if it'* the problem is to replace it. However, you can try removing it, spray a little intake cleaner in it, and shake it out well, When you put it back on, put some silicone grease on the vacuum fittings to try for a better seal.

How does the filler neck look? I had a similar issue that replacing the gas cap didn't correct. The lip on the filler neck had a little bit of corrosion on it so the cap wasn't sealing properly. Cleaned it up and it'* been fine for almost a year now.

I've been following this one...

I don't want to oversimplify and I am not that familiar with the differences on the 2000+, but I can tell you that after chasing all kinds of things on mine (yes, it was only a '97...), The real culprits of my P0440 code were small cracks in the evap ine connectors. the rubber connnectors were craked ever so slightly, but add them all up and I had poor running and a CEL.

It won't cost you anything to carefully inspect all the evap lines and any connectors or lines that need replacing can be done for very little out-of-pocket.

Worth considering, IMO.

Thanks, I actually have done that too - I even went as far as polishing the lip first and putting a small amount of vaseline on the cap to help the seal.
It seems it may either be one of the solenoids or yes possibly bad tubing.