If your keg was used for soda syrup at one time, replace the seals before you use the keg to prevent the transfer of soda flavors to your brew.
After you replace them, maintain them.
As quick-disconnect fittings are attached and removed from the keg poppet valve, the fittings slide over the oversized o-ring on the outside of the valve assembly.
Without any lubrication, o-rings can get torn and wear out early.
Since petroleum-based lubricants attack most rubber materials, non-petroleum lubricants are needed.
Available through ausie spirit & homebrew who handle beverage equipment, Keg lubrication looks and feels like a lightweight grease but is safe for food contact surfaces and o-rings.
A thin film of Keg lubrication applied to o-rings makes it much easier to attach and remove quick-disconnect fittings without harming seals.