V-in-LA, You are correct to advise on the Viton o-ring but I would like to know why you feel the nitrile o-ring won't last in the 1100 application.
The Viton is more heat resistant and impervious to more chemicals then the Nitrile but I've not found a gun cleaning or lubing solution that negatively affects Nitrile.
Also Viton is not really recommended with ester or ether solvents and if I remember correctly, cleaning solvents such as Hoppe's #9(and some others) falls under the ether solvent list.
Nor do I shoot my 1100 enough to generate enough heat to distort the nitrile o-ring.
Too, about 4-5 years ago, I ordered o-rings from Rem. for my 1100's as well as two of my brothers 1100's. I was sent a packet of 10ea.(if I remember correctly) o-rings which were silicone o-rings. Was a bit surprised and didn't use them.
Went with the nitrile instead.