P0440 code

2001 Buick Le Sabre, I've had the DIC tell me I have a loose gas cap P0440,when it first happened my mechanic took it to the shop and checked the system and then smoke tested it and found nothing,it was good for 3-4 months and came back,then I purchased a scanner for myself and checked what I could and only found some pitting on the filler neck(very slight) so I smoothed it and reset the code,it lasted 2-3 months and is now back again.Is there something that I can check on my own because the factory service manual is a long process to troubleshoot this code or should I leave it for the pros?

unless you have a smoke machine there is not much you can do.

Happening every 2-3 months, or 3-4 months, is very intermittent....

Is it possible, this is happening because when you get a fillup at a gas station, the attendant does not click the cap properly?

If it was a component problem, it would happen much more often during a drive cycle....