I'm familiar with the WSK gasket and does have an interesting way of attaching it. if I had an issue with mine, I'd contact weber support.
If weber support didn't pan out, I would replace it with a Rutland gasket glued to the lid using RTV ultra copper.
As I mentioned, I replaced mine on my large BGE a few years ago and it is working great.
Ron Pratt aka "RRP" on the BGE sites was an early advocate for using Rutland gaskets, and sells them for his cost plus shipping. I don't like to cross-post to other forums but if you search for "Ron Pratt Rutland" you'll likely find his contact info. Last time I saw a post on the BGE forum he'd sold over 7K gaskets just mailing them out.
I don't have an XL BGE to compare with, but the size is probably pretty close as the XL BGE has a 24 inch grate like the WSK.
Best of luck.