Sounds like you have tried everything! Just to let you know, I had a similar problem, same as you, had it all on and off several times, only to find it was the sender on top leaking and dribbling down. It only did it under load, not on the ramp at tickover. Finally found it by having a handy helper on the throttle and me underneath! It had me fooled for quite a while. Might be worth checking.
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