I bought a "door-window frame to top-door" seal from 914Rubber. It's all one piece. The frame to the forward edge of the door/side windows, each side, goes in easily. It is the horizontal, leading edge of the top to frame seal that is giving me fits. There is a "C" shape that fits over the knife edge of the frame.

I read somewhere that you just have to push very hard on the back of the "C", that is, the whole seal, to get it to stay on the knife edge. I can't push hard enough apparently. I have Vasolene all over, too. (Had to get the rubber part of the seal back to surrounding the metal "C" thing that goes inside the rubber.) Is the Vasolene preventing the seal from sticking or snapping into place? There is no barb or edge on the frame/knife edge to grip the seal. What holds it in place?

Need some advice from someone who's done this. Thanks in advance.

DO the sides 1st then the top starting at the center. The clip is tight so if you need to you can open up about a 2" section of the top seal by pushing in a screwdriver (flat). Do not twist. This will allow for you to start the seal. Using warm soapy water will help also.
It is possible the clip is not fully engaged as it is tight. We made it this way as the complaint was it would come off with the top if the top had been on for awhile. Soapy water or glycerine work well to help persuade it all the way on. You can use a large flat screwdriver to open up about 3" in the center of the top. This will allow for you to see it fully engaged and help it to slide on. I prefer to install the sides 1st athen the top from the center so it's not stretched one direction too far leaving too much material on one end.
Yes it is normal for it to be difficult to engage. I didn't see the pictures, but if the seal isn't sitting on the front edge, it's not fully engaged. Pop it back off as it's not all the way on (only the top section). open up the center 3" or so with a flat screwdriver so you can start the seal. Lubricate the seam it sits on with soapy water. Then take a wood block and a rubber mallet to tap the seal on. If you have second set of hands to grip the seal pulling it in while you tap on the block you should find it can be persuaded into place.
DO BE CAREFUL when removing the seal, and when installing that the metal clip is not pulled out of the metal and it is not binding as you are trying to install. The latter is a matter of it not going squarely into the channel. It can be corrected, but why create more work if you are aware of a potential install pitfall.
Follow up on adhesive use -
The main targa seal has the metal clip that needs to go over the pinch welded lip. The problem is that if it's not tight it will pop off. The technique is to open up the center 2-3" using a flat screw driver. This allows it to start onto the lip. The weather-strip adhesive is if the metal is a little lose to hold it on. You should be able to install using soapy water to allow for lubrication (glycerin also works). It is imperative that when you install it you do not pull it as it will stretch the seal leaving you more material that can fit.. This will require removal and reinstallation and once the clip has been widened it may be more prone to come off with the roof requiring the adhesive. If adhesive is required you can put a few 1" beads just on the top of the welded seam. I use recommend the 3M weatherstrip adhesive as it will stay somewhat tacky and is easier to clean up.

Using glycerin rather than vasolene makes for an easy clean up. Just water and a soft rag. You can paint it on surfaces with cheap foam brushes.

..........this would be nice to have as a DIY picture guide

Thanks for the replies, guys. Don't know what I'd do without this community.

I will pick up some Dawn to try to clean up the Vasoline and to lubricate the install. I have every solvent known to man for that, too. Maybe I'll try some glycerine, too. I have a rubber mallet, wood block, screwdriver, etc. Starting the top at the center makes sense. Getting the metal back into the rubber after failed attempts is a bit**. I'll post how it goes.

I'd rather have it too tight than the other way. Looks to be a quality product, but I can't rest until it's on.

UPDATE

North Coast Jim provided some helpful advice. He installed the seal using a block of wood and a rubber mallet. I used glycerin, got it lubed up, started at both ends then began at the center. A couple of good whacks every 3" got it to stay in place, but look at the results. Did I get it too far on? Some places it looks perfect but at others it is sticking up and I can't get it down. I don't know whether or not to pull it off (that will be a bit**) and try again using the same seal or to order another and start over. Any advice? Click to view attachmentClick to view attachmentClick to view attachment[attachmentid=612
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Ordered a second one and will try again. More lube and a little less pounding, I think.

Got the second seal on. Thought I had it on but the corners weren't right. Ripped it off and started over. With the glycerin, the second time the sides slid right down so the corners were right. Centered it horizontally. Tapped in on with a rubber mallet starting in the center. Came out fine. Good product.