| Drew,
Did you do a compression check of the engine?
A fouling plug can be from a variety of individual failures or the sum of several lesser problems. A poor spark will certainly bring about fouling of the particular plug. Seems odd to me that you have been in and around this engine for the last 6 months or more and just discovered it has a fouled #1 plug.
Low compression will also foul the plug. Low compression can be the result of a burned valve (which could be from a bad lifter), a cracked head, bad head gasket seal, or some condition relative to the piston ring and cylinder wall interface. And, a bad plug wire leading to poor spark, leading to poor combustion, leading to filling the compression rings with crud can all conspire to make a simple problem worse.
Anyway, I would do a compression test and find out if #1 is significantly different than 2 through 4. If you have already done this, I missed it in your list of events.
Jim | 
