1996 850 gas smell after engine stops running and/or a full tank fill-up

Our 96 850 has about 87K miles and has gave us a strong gas smell
after
the car is driven into garage, parked, and stopped in last month. We
have tried
to found out where the gas smell came from w/o too much luck, though
it is
pointed to left front of the car, and right rear of the cat (fuel
filler
area). But, we could not spot a sing of fuel leak at all.

The gas smell is extremely bad with a full tank fill-up. The garage
smells
like gas every where. I saw small amount of fuel leak around the clamp
of fuel tank and fuel filler neck. I removed the clamp and cleaned
out the dirt, did it second time to clean the fuel neck and tank
contact
surface for any possible dirt. (I had to loose the fuel neck at fuel
filler
door and had my wife pull the fuel neck some so I could cleaned it.)
It did
not leak for a while until yesterday. With a full tank fill-up, I
could see
the fuel tank was wet with fuel around the clamp area again!
(Naturally, there
is gas smell in the garage.)

I removed two covers in the trunk to access fuel pump and tube
connections area of the fuel tank, and found no fuel leak or wet spot
there.

I called my Volvo dealer, a technician told me there is a gromment
(gasket
or O ring type of material) between the fuel filler neck and fuel
tank, to
prevent it from leaking (Volvo part #6842188 $13.51). My problem is
that I did
not see this gromment while I cleaned it twice. Would the gromment
shrink
after 8 years of service? If there was not a gromment before, why it
was not
leaking fuel before? Was this a real problem?

It seems that the fuel tank, fuel pump, fuel lines, etc. all have be
removed
to remove the fuel tank to install this gas tank gromment. Is it
correct?
Is there another way to fix it?

thanks and best regards,

Joe
1996 850 87K