Odd starting problem

Perhaps somebody here has an idea about this little problem.

A few weeks ago, shortly after annual, I tried to start our Cherokee 140.
It kicked for a few revs, and then failed to start no matter what I did.
I noticed the aux fuel pump kept pumping, as if it was not building
pressure. The primer seemed to have fuel. I noticed fuel on the carpet
and leaking outside below the aux pump. We had our mechanic replace the
aux pump gasket a few days later. I then flew the plane twice after that
without any problems.

So today (a gorgeous day, by the way), my partner and I are going to fly.
We try to start the plane and it kicks once, then fails to start. We try
more primer. We try flooded procedures. Eventually the plane is cranking
slowly due to weakened battery. We get the car over and jump the plane.
We try everything. There is no fuel leak anywhere. There is no smell of
fuel anywhere. Aux fuel pump keeps clicking as if pressure is not being
built up, but no leaks. Primer feels like it is pumping fuel into
cylinders. Sumping fuel reveals no water. We try switching tanks. Once
the first kick happened, NOTHING would get it to fire.

So we're planning a long XC in a couple of weeks. I'm concerned that even
if our mechanic does something, we might still not have it fixed and then
we could get stuck at some podunk airport. Although I thought the problem
had been fixed previously, the symptoms are the same, minus apparent fuel
leaks anywhere.

It acts like it's not getting fuel. The fact that the initial crank fired
suggests it's not electrical. But the fact that the primer feels like
it's pumping fuel means it should fire after priming, at least for a bit.

Anybody have good ideas?

Thanks in advance.