Best thing is to get it on a lift and follow the trail to the highest point if you can. Or just get it as high as you can on stands and use a really bright shop light.

As for that plastic tube under the car. I do beleive that is the drain tube for the duct work in the car for when condensation builds up due to the A/C. If fluid is coming from that I would have to assume that the heater core has developed a crack or something along that line.

If that is the case, its gonna suck getting that out. I can do the job for you. Since its such a pain in the neck Ill do it for a small fee.

EDIT: Just noticed you are in the 757 so n/m about the job.