Last time out when the tanks were almost full I thought I smelled that unmistakable odor coming from the closet. Very faint. Anyhow, i replaced all four air admittance valves with Studors just in case. Most of us just buy the Home Depot variety which are much cheaper but I had one of those fail in the past so I stick with the Studors.
jor
I agree the Studor looks and feels like it is made better I used them in mine also.