Quoted from vid1900:
First I'd get my meter out and with the board unplugged from the harness, see if the transistor reads differently that the other ones next to it. If it is different, I'd replace it.
I spoke to Ed @ Great Plains, and he recommended an IRL 530n as a suitable replacement. I also had a chance to converse with the Kohout brothers down in Texas, and they responded very quickly. They indicated that likely the mosfet was likely toasted, and that they could either send me a new one, or I could opt to send the board in and have them repair it for $20 bucks including return shipping. I thought this a very fair offer.
I am going to be brave, and attempt the repair myself, using the IRL530n GPE will send me..... Their boards are clean, and easy to work on. If I fail, I will send it back. I won't fail!!!!!
So by this weekend I should be able to report back if I can get the pop bumper running again..... Fingers Crossed!