Another anecdote to justify Ron G's comment:  I had a Cardinal and I smelled fuel only on final with the gear down.  I inspected all the fittings and found nothing.  There was no blue stain anywhere.  But then I noticed that the engine, which had always leaked oil, was cleaner than normal.  Hmm....  I finally turned on the fuel pump and started pressurizing the fuel system by pushing in the mixture.  If I bent the flex line to the fuel pressue sensor - bingo.  It must have been leaking a lot to wash out the engine compartment that well!  Yikes :-(.  The flex line to the fuel pressure sensor is dead-headed, so no fuel flows in that line and the trapped fuel eventually turns to "sour gas".  That line is usually the first to go.

FYI

Gary Casey