How can I join vinyl decking to metal door frame?

Question

Shoddy workmanship by a lousy contractor has left me with a vinyl deck that allows water to leak into the garage below. I identified the location of the leak - where the vinyl meets the metal frame of the sliding door. He had put some caulking over the joint (not visible in photo, removed by me) and then screwed a thin metal cover across it, but this "solution" failed to keep water out. The caulking had split in several spots along the gap, and it didn't seem to have cured properly on the vinyl (dry to touch but sticky/gooey when manipulated).

Is there a proper way to seal this gap that will withstand the elements (northern climate, snowy winters, sun-facing)? I thought maybe fiberglass tape and roll-on rubber or vinyl coating but I don't know if it will stick to either the metal or the vinyl... help?

EDIT

The deck is about 1/8 inch lower than the frame on the left side, and flush on the right side.

Head-on view:

Entire length view:

Answer 1

Based on questions answered in chat you have a case where the contractor didn't measure the deck properly, and built it too high, could not flash properly under the door frame, and performed a "some genius" move putting a transition strip (meant for interior use) over top of the door frame and the vinyl, with caulk under neath.

Stupid.

Two options: 1 cheap and temporary, 1 expensive and proper.

Cheap: Use proper caulk (props to @tester101)

Option 2 - and the door is old so this isn't actually a terrible idea.

Replace the door. In the process, raise the rough opening of the door frame half an inch or so - however much is necessary to be able to put a proper piece of flashing under the door frame and over the vinyl.

You will probably have to custom order a door to fit your new rough opening, but at least you can seal the door area properly.

And props to @bmitch for pointing out that flashing needs to run the entire width of the deck.

Answer 2

In regards to flashing the full width of the deck:

Instead of flashing the entire width of the deck, usually the vinyl would go up the wall several inches. If this is not the case, and there is also no flashing, I would call a vinyl guy (not the same one who is responsible for this atrocity) to come in and do that. they should be able to look after this, heat-welding vinyl-to-vinyl, and use some good sealant at the doorway seam and do a better job and use a better product than most homeowner specials. Below is an image of a this after I reinstalled some of the siding, but you can still see how the vinyl goes up the wall.

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In regards to caulking as a solution:

Just to reiterate that there is no cheap way to fix this properly at this point. Whoever built your deck is not someone who should be charging people since they have no clue what they are doing.

You can use caulking for a temporary solution but you should know that it is something you need to check and replace as necessary.

Even then you should keep in mind that even if it looks okay it might be letting a small amount of moisture in that won't show up as a visible leak but can cause rot in your framing over time. I do a lot of repairs where this is the case.

Caulking being relied on for waterproofing usually ends up as an expensive repair at some point.

May be many, many years later, but may also be sooner than you wanted.

I have many photo examples of this, but here is my current project. A roof-top deck where caulking was relied on for sealing flashing seams.

Here is a beam underneath a sliding door at the corner of a house. It had sunk over 1/2" inch and was being held together by magic and pixie dust™. (the new section is what I added in while replacing.)

I have tons more, but this should be enough to reinforce the point.

Caulking is never a "fix", it is only a band-aid solution that will help delay or prolong the inevitable result of poor workmanship.