Resealing of a window

We need to reseal a rear window tomorrow when the rain stops. There is a small leak and I believe it's coming from the window.

1) Do we have to try to get all the old gunk off/out before we put new gunk on in order to get a successful seal?

2) What product would you use for this type of thing, and how much is needed?

I did a little research and saw that you should clean the area, put more gunk on it and push it in with your finger.., but different sites suggested different methods. Thank you.

I found this video.., it may be helpful to anyone else who has never done this.., it seems very simple:

http://www.youtube.com/watch?v=4UL1ig8gnwg

I just had this discussion with my trailer repair guy.  In order to get the factory sealant off he uses a small piece of plexiglass which he grinds a somewhat sharp edge on.  This way he doesn't badly scrape the metal side of the trailer.  I was wondering about using a plastic putty knife instead for the scrape job.  But haven't tried it. 

I was going to buy a new putty knife today with the rest of my supplies so I'm glad you suggested that.., I think I'll buy both and see how that works.

So, of course it was harder than it looked on the video.., but still an easy to handle project for the two of us.

We found our leak for sure.., once we took the window off you could see a crack down the siding.., it looked like someone had screwed the window in too tight or something and it just cracked the siding where the two met. You could see where it was wet from the top of the crack down. The crack started a little above the window and went below it too. We chose to seal the crack with eternabond and then resealed the window. You can see the tape along the side of the window, but we used tan eternabond to match our tan siding and it does not look too bad.

You could also see where someone had tried to fix it before but all they did was make a silicone mess.., a good deal of time was spent on removing old silicone.

A tip to anyone doing this for the first time..., we wasted about 18 inches of butyl tape trying to peel it off the paper instead of using the paper to peel it off the roll. This would make more sense if you had a roll in your hand. I thought we had a "bad" roll of tape because it seemed "squished" into the paper and wouldn't peel off right..., then I realized you are supposed to use the paper and "double unwrap" it and it comes off the roll very easily. At least we didn't waste too much.

It feels good to have it done! I think we did a good job, it looks like the seal is very complete and with our crack fixed I think we'll be dry now.

Glad to hear you found and fixed it. Good luck!

It was raining pretty hard the last couple of days..., and it worked! Not a drop of moisture under that window frame anymore.

Well, none there.., but a bathroom vent we did is still dripping.., guess we'll be back on the roof soon.

We did a good job with the eternabond bond so it may be the vent cover or something.., we'll need to look again. Everything else we sealed is working well. Lucky for us the water from that bathroom vent drips directly into the toilet.