Please see this thread:
http://www.automotiveforums.com/vbulletin/showthread.php?t=327245
Thanks.

There must be more people out there with this problem.......

How much feedback do you want before you choose to replace the gaskets. Sure my 1998 5.7 leaked at the same place (the rear gasket, which keeps the coolant out of the lifter "valley). I did the same thing replaced with felpro and Ultra Black sealant. Been perfect ever since, why would you let it go? It can easily turn from a gasket replace to an engine replace.I didn't anwser your post before because it seems reapetitive.The other guys replys sums it up.

I've seen oil in the coolant reservoir of some 4.3L S-10s. I would replace the gaskets, flush the system and switch to the red stuff. Plane on doing it to mine.