Good call replacing both cylinders. You can search and find numerous threads where people have replaced one and the other failed soon after.

The gasket is probably there to prevent the cylinder from rusting to the firewall... This is just a guess on my part. Also seals out water and brake fluid (though not completely if the cylinder fails, as you saw).

08/13/11 - a/c repair redeux
 

So let's give this another try.
http://i59.photobucket.com/albums/g2...1/IMG_0023.jpg
Out with the old.
http://i59.photobucket.com/albums/g2...1/IMG_0025.jpg
New pipe without the worn away hole. Being busy with traveling and work, I decided to just get a new hardline from Net Seven here on the forum.

http://i59.photobucket.com/albums/g2...1/IMG_0026.jpg
Another round with the air box. I really need to find something else or convert my setup.
http://i59.photobucket.com/albums/g2...1/IMG_0027.jpg
Lines going into the car ready for the new o-rings. Such a pita to get to. ABS module is in such a bad place.

http://i59.photobucket.com/albums/g2...1/IMG_0028.jpg
http://i59.photobucket.com/albums/g2...1/IMG_0029.jpg
http://i59.photobucket.com/albums/g2...1/IMG_0030.jpg
Next up is the replacement of the old drier. Always essential in repairing an ac system that's been exposed to the air. I also guess the previous person working on the car was a smoker.

http://i59.photobucket.com/albums/g2...1/IMG_0031.jpg
http://i59.photobucket.com/albums/g2...1/IMG_0033.jpg
http://i59.photobucket.com/albums/g2...1/IMG_0039.jpg
New drier with incorrect o-rings. More to come.

08/13/11 - a/c repair redeux - 2
 

http://i59.photobucket.com/albums/g2...1/IMG_0036.jpg
http://i59.photobucket.com/albums/g2...1/IMG_0035.jpg
http://i59.photobucket.com/albums/g2...1/IMG_0038.jpg
So this red nylog o-ring lube is pretty similar to the consistency of nasal fluid drainage. It was quite interesting to work with.

http://i59.photobucket.com/albums/g2...1/IMG_0040.jpg
http://i59.photobucket.com/albums/g2...1/IMG_0041.jpg
http://i59.photobucket.com/albums/g2...1/IMG_0042.jpg
I also added about 1oz of mineral refrigerant oil to the drier. So all done and ready to go after an hour. My shirt still got soaked after only an hour of early morning work.