Gas and Oil Home Heating Furnaces - Chimney leak

My wife and I have purchased an old farm house (+100yrs). I t has a chimney running threw the middle, from the floor of the basement, to the roof (2 floors). We installed a 90% efficient gas furnace using the chimney for exhaust vent (lots of up draft). About a month later a dark liquid started dripping down the outside of the brick chimney. Since the roof was visably leaking around the chimney, I went up there finding the bricks were soaked and would crumble easily. So, we removed the bricks down to about 3' below the roof line, and added "B-Vent" from that point upward (w/ collar and rain cover, and shingles, etc). We can find no leaks from the roof now (thank God), and the top 4-5 rows of bricks are dry now, but the next 8 feet of chimney bricks are oosing with this dark liquid still. We have pointed a fan at the 8 foot section, and placed one at the cleanout door to try and dry out the bricks. What is going on, and what can we do???
The leaking began at the top and has moved down the chimney, so we thought the brick was soaking up the precipitation. It is only leaking on the second floor now, which is not heated yet. It does not leak at all on the first floor (heated), or the basement (unheated).?????

You can wait for a gas person to respond also but I can tell you what the problem is. Condensation. I have the same problem with high efficiency oil boilers and there is only one way to resolve it on oil systems. Install a stainless steel liner in the chimney. For your purpose, there may be more options. One would be to vent out the side wall. You probably have an induced draft furnace, so you don't need any external draft source anyway. Or you could install vent pipe all the way up the chimney (if it wouldn' exceed the mfg. specs for length) and let it vent out up there. Forget making the condensation go away any other way and be sure to do something about it as soon as possible because it is acidic and once it starts attacking the chimney, it is tough to get rid of. Good Luck.

should be pvc if it is a 90% furnace from the furnace to the termination above the chimney. if you are saying the unit is vented into the chimney with no pvc going up, it is violation of code, installation instructions, and can void your warranty. sidewall ventilation is an option.

:) It requires a 3" B-Vent exhaust, as per instructions. The 95% was the one requiring PVC only...