I am wondering if these GM minivans have a common failure point for a
small evaporative control leak detected.  I've tried two brand new fuel
caps, first a Stant and then a Genuine AC-Delco.   When I clear the code
it goes away for a short while, but comes back within five or so driving
cycles.

I have a code reader, but I don't have one of those nifty smoke machine
leak detector set ups.    Is there a common failure point which usually
is the source of these leaks?

Also, this started happening right after a local dealer butchered the
car while replacing the A/C condensor.  For example, the two screw type
band clamps on the air duct work from the air cleaner to the intake were
loose. The also didn't bother to put the caps back onto the A/C pressure
test ports.  Luckily the caps were still sitting on the cowl so I could
clean them off and re-install.  They also left the coolant level low and
didn't bother to reconnect the various clips which dress off the wiring
harnesses.  All in all it was the kind of butcher job one expects at a
fly-by-night shop, not a "Goodwrench" dealer.

Any help pointing me in the right direction on the evap. leak would be
appreciated.  I am going back to my fix-it-myself policy after the
disaster of paying $1000 to have a dealership due a crappy job.

TIA,
John