Need help with a problem in our PA28-140

We have a really weird one and I'd like some help in the diagnosis.

We're in Southern California and have a 1974 Cherokee Cruiser with the
O-320E3D.

Background:

About a year ago we had our annual. During the annual our mechanic took
apart the gascolator and checked/cleaned the area.

We flew the plane home from the "annual" field to the "home" field
without problems.

In the next flight or two, we had a situation that would repeat itself a
number of times in the last year: During an attempted cold start, we
would primecrankfiredie. The primer appeared to burn off and then
nothing would get the plane started.

I noticed that when trying to start the plane I heard the aux fuel pump
continue ticking as if pressure couldn't be maintained in the system.
Additionally, there was some gas inside the plane near the fuel tank
valve. Our on-field mechanic checked the plane and removed and
reassembled the aux fuel pump, cleaned out the primer lines, and rebuilt
the mags which probably needed it anyway.

One item was that this starting problem happened after a rain.

During the summer, we had an uncharacteristic rain. My partner tried to
fly and the same primecrankfiredie sequence occurred. He pulled the
plugs and found what appeared to be water in them. He cleaned them and
put them back in, and the engine fired up and ran normally.

Forward all the way to a few days ago. The plane had been down for a
nose strut rebuild, and my partner flew the plane afterwards. The next
day we had a very small amount of rain. I went out the next day to fly,
having been grounded for the strut repair for a few weeks. Since it had
rained and I suspected rain might have something to do with the starting
problem, I made sure and sumped both tanks and the gascolator. No trace
of water.

The same sequence of primecrankfiredie occurred with me. After this
happened I then re-sumped everything and still found no water. I did
notice that once I couldn't start the plane, the aux fuel pump kept
ticking as if there was a pressure leak in the system. I looked under
the engine and saw some fresh fuel under the carburetor on the nosewheel
pant. Since I didn't have any tools with me to pull the plugs, I gave up
for the day.

A couple of days later my partner went to the plane, pullled the plugs,
and found water. He dried the plugs and the plane started right up.

Observations:

- This has only occurred after it has rained
- When it occurs it seems that the fuel pump cannot maintain pressure
- We've seen some fuel leakage but no consistency here
- We've had it occur even though we don't find obvious water in the
system
- The two times we've pulled plugs they appeared to have water on them
- When it hasn't rained the full starting sequence has been normal and
we've seen no fuel leakage

Based upon this reocurring problem, we've put some tools in the plane so
that we can always pull the plugs. Yet I don't really trust flying the
plane a long way or especially if precipitation is forecast.

Anybody have any ideas on what could be happening here?

T. Long