Just did this today as part of my 24,000 mile service on my 2008 R1200GS Adventure.
[As an aside, what shouldn't be all that much of a service is turning into a major affair. I'm also replacing a ton of badly corroded bolts, and while I have that much of the thing apart I'm taking out the OEM ESA suspension and swapping in the Wilbers I've had on the shelf for a rainy day--actually, rescued from my old '05 GS that I traded in for the Adventure). ]
In any case, I just wanted to note that on the '08 Adventure the gas rings are both located on the top front of the gas tank, with one disconnector on each side. The left ring has the fuel pump, based on what appear to be heat-dissipating fins, and not really sure what the right ring does, but each had one quick disconnecter.
I didn't have any cracks visible, but one of the plastic disconnectors broke in my hand when I gave it a moderately forceful bend.
Glad I have the steel ones on there now.
All in all not too difficult a job at all.
Now, back to my rusty bolts.