'04 Tacoma 4WD Xtracab Rear Diff Front Oil Seal?

There is one heck of a mess underneath my truck bed. It is all over the place, including the bottom of the bed and the bottom of the fuel tank. I suspect it is the rear differential front oil seal leaking. Has anyone dealt with replacing this seal? I looked it up in my factory shop manual and it involves removing the rear prop shaft and then you need a whole bunch of special service tools (SST)s to get at it. Most worrisome for me is the SM discusses setting the pinion pre-load. I talked to the local Toyota dealer and they want 3 point something hours (= $550) just in labor. I discussed the job with the lead mechanic and he said they have had success just replacing the seal itself and leaving the bearing/spacer alone. I don't know if that makes sense to me.

 

Any thoughts guys?