I'm bumping this since the same thing happened to me today. Being a dedicated BITOG type guy, I abandoned the standard fuel oil filter a few seasons ago and installed a dual Permacool setup with some WIX 33281 filters that are 3/4-16 thread. I went to NAPA on a Saturday and they didn't have them in stock (they used to) and he quoted me list of $17.xx each. I really think that they have different prices when the trade isn't paying the bills. I can walk in there during the week and get decent prices ..on the weekend ..nope.
Anyway, I ordered them from Fleetfilter for under 10 bucks each ..but they haven't arrived yet.
So ..a ST3600 is on one of the filter positions until they arrive. I think I'll be okay until the 10um filters arrive. For all I know ..they finally filled up with water. The filters (this particular 3/4-16 thread diesel fuel filter) doesn't have a water tap.