Question for an electrician/person who is handy

[MikeyC]

So, I've been living in the same condo for the last 2+ years and during that time I've been using the same electric (yuck) BBQ on my deck the whole time. The outlet I plug the BBQ into on the deck is connected to a GFCI outlet in my guest bathroom (the master bath outlets are also connected to the same GFCI switch). Starting about a month ago, whenever I would use my BBQ the GFCI switch would trip. It doesn't trip right away. It trips after the BBQ has been on for a few minutes.

The building is almost 30 years old. So, I decided to start replacing some pieces to see if that would help. First, I tried changing the extension chord I was using with my BBQ. No change. Next I tried replacing the GFCI outlet. That didn't make a difference. Tonight, I tried replacing the outlet on the deck. However, the GFCI trips. I also tried unplugging everything in the bathrooms while running the BBQ, but still no luck.

The good news is I've got a new GFCI outlet, a new extension chord, and a new outlet on my deck. The bad news is that my BBQ still doesn't work. Logic would dictate that the problem is either with the wire inside the wall or with the BBQ. As I'm no electrician, I thought I would solicit opinions to see if anyone had any other ideas before I buy a new BBQ or have an electrician rip open the walls of my home.