I did a little piece on that in my resto thread... Metro makes a good seal and I suspect that you may not be installing it correctly so that it holds in the channel.
Heres an excerpt from my thread that may help....
The upper window seats into the hardtop window seal such that, as the door closes, it must be able to pop the window up and into the seal and have the seal engage the top of the window glass. I know I've seen a section illustration of the seal in the open and shut position that makes the above easier to understand. And if I can find it again in the FSM I'll post it. But, the last bit of travel as the door latches must be able to push the top of the glass up into the seal such that it deforms and forces the seal to roll over the top of the glass.
The seal should have a continuous lip on the outside for the top of the glass and edge on the inside that needs to mate to the edge in the channel to form the outside "roll over" seal for the top of the glass....
Make sure before you start installing the new seal that all of the old seal and any old glue is completely removed.
I started by test fitting it without the glue first til I was comfortable in my technique. The seals should be about 12" or so longer than you need for your car so check that it is and if you can, cut off a few inches to test your install. I did this because my seal kept falling out and i couldn't figure out why. It was then that I noticed that the seal needs to be set into the channel in a certain way for it to stay and work correctly. With the small piece in to test fit first, the rest of the instructions should then make sense because you will be able to see it in in the channel from the ends...
Also, once fully installed without the glue, I left it out in the sun for a few days so the new seal would take a set to the channel ( I wasn't in a hurry). I installed mine a few inches at a time starting at the front of the door where it should clip into a hole meant to hold the seal tight. This first few inches I did glue in before attempting the rest of the install without the glue.
First I put the seal so that the inner edge of the seal and channel edge mate. This edge (or lip) is on the flat part the sets to the body and is not very deep (about 1/16"). This is the most important part of the install. This edge on the seal and the corresponding edge in the channel must mate up perfectly for the top of the seal to be able to roll over the top of the window glass and get you a good seal. once these two edges are mated and while holding it it place with a 6" piece of 1/4" dowel ( a pencil without a point would also work) I then worked the top of the seal into the channel with a small dull 1/2" wide spatula or other wedge tool. If it slips out, don't worry, you didn't glue it in yet. If you did it right, the seal will hold in place leaving the thin rubber loose at the base of the seal to cover the interior trim.
Another way that might work better for you would be to push the top of the seal into the channel and force it up until the inner edge of the seal and channel mate.... This is a bit harder to do but would work the same and is useful to know if a portion should slip out after you set it.
Once in, it will look flat with the top edge sticking slightly out past the chrome trim of the channel.
good luck!
