Dead 912UL Fuel Pump Pass Through

The small amount of fuel in the pump smelled odd.  This fuel was unleaded, ethanol-free RON 92 gasoline (mogas).  It had been in the pump for about six months, during which time the aircraft was shipped from SE Asia (hot and humid) to Florida.  I recently disassembled the pump (after gently heating the housing to free the force fitting holding the pump components.  The layer of slime was no longer visible on the plastic screen. Air passed freely through the screen. So the gudge was volatile, whatever it was.  I think the lesson here is that next time I will drain the pump, or at least flush the fuel lines with avgas.  I had removed and dried the carb float bowls prior to shipping because of en earlier experience with fuel gumming which caused the floats to adhere to the bowls.

Good point on fuel line flushing--I did all of this, cleaned the gascolator screen, etc.  And then I flew!  All good.

"translucent, jelly-like contamination"

What is the cause of this ?