Slight gas smell from boiler at ignition and shutdown

We just bought this house and I noticed that if you have your head down by the igniter/jets of the boiler you can briefly smell gas when it kicks on and for a few minutes after it has shut down, but never while it's burning.  It's an older dunkirk model boiler.

Within maybe 5-10 minutes of being shutdown the smell goes away completely and doesn't come back until the next ignition, goes way while burning and briefly comes again after shutdown.

I have a handheld gas leak detector and it's enough to make it go off if held down there during ignition, and for a few brief seconds after shutdown.

Any thoughts would be appreciated, as i've never owned a gas boiler before and it's kind of freaking me out!