Are you sure it's not coolant? Does the odor come out the vents with the heat on? Sounds like a leaking heater core or bad hose.
There's another drain for the air vent entry. That's the grill area between the windshield and hood. If that drain is blocked, the air intake area will fill with water and flow into the vehicle through the vent. This one is a bit tricky to find under the vehicle. You may be able spot it with a flash light while looking through the grill. It's usually on the passenger side.
Odd that Ford can't find the cause, but I bet they charged you $100 to look for it.
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Good Luck...
mj
'01 Ford Ranger 3.0 Super Cab, K&N Air, MaxFlow Exhaust, Oversize Tires 
'93 Ford Taurus 3.0 (Ugh! What a MONEY PIT! Traded it in for the '01 Ranger) 
'87 Ford Ranger 2.3 Super Cab (Owned it for 16 years until some clown t-boned me in it!) 
'92 Ford Aerostar 3.0 (Gave it to Ex in Divorce Settlement) Hehe...
'74 Ford Maverick 250 ci (Great car! 110 mph on Autoban! Traded it in for the '87 Ranger)
'66 Ford Mustang 200 ci (Screwed up and SOLD IT!!)  | 
