Smell from chimney which has been capped plus complications

My problem touches on building, chimneys, roofing etc. I very much hope someone can help. Thanks for reading and if moderators wish to move to a more appropriate area then no worries and thanks.

1998 - My parents fitted a gas hob into the fireplace in the kitchen and fitted an extractor (no chimney lining) to take cooking fumes up the chimney

February 2012 - Our new kitchen was fitted and we were told we could not extract up the chimney, so our builder drilled through the side of the chimney, just above a new extractor, and fitted an exhaust to the side of the house.

Christmas 2012 - In the horrendous weather of that year unpleasant brown liquid seeped around the board where the extractor is fitted and run into our kitchen. It smells ghastly, (rather like you might imagine water would smell if it had dribbled over 14 years of cooking deposits in a chimney )

Christmas 2012 to July 2014 - The problem remained but was tolerable. We saved for a new roof and chimney removal (which needed doing anyway)

July 2014 - New roof fitted, assumed all was groovy, however, unpleasant smell still appears. I think it is worse when windy

There is a vent on the first floor bedroom which smells, and the area around the extractor smells.

My current inclination is to firstly remove the vent in the first floor bedroom and have a look. If I learn nothing, I plan to remove the chimney from the new roof down to the floor of the attic and have a look. My final plan is to rip out the extractor and mounting panel and push one of my children up the chimney with some Cillit Bang.
As you may gather, I am very much clutching at straws and would really appreciate any advice
Thanks in advance
Tom

Tom, has your extractor hood got any sort of ducting fitted to it? Absolutely essential, that one.
I'd be inclined to cap the chimney but to insert ventilation bricks at the top and bottom, to keep it dry.
John

Hi john
Thanks for your answer. The extractor is ducted through the side of the chimney just above it, along the wall of the kitchen (through a wall unti) and out the side of the wall to the outside.

I see.....look at the duct termination on the outside (louvre vent, maybe) and see that the duct is still connected inside.....it's not unknown for them to come adrift. The same applies at the top of the extractor, if possible.
Is there any way that water can get into the louvre?
What's the pointing like on the wall gable end?
John

You would need a commercial steam cleaner up the chimney to shift that amount of kitchen grease and grime.

Thanks Burnerman. The gable end is fine, however, the internal ductwork is an interesting and new thought. As the smell appears worse when the weather grim, I favour ideas linked to the extractor / ductwork.
As wife is away, I will attack this over the next few days.
Thanks for the thought of commercial steam cleaner foxhole. I have added it to the ever growing list of "Very unpleasant tasks to do when Eastenders is on"