I've had a few failed attempts with Dawn, even with three people.  The last
corner would just not go in far enough, and I didn't want to risk breaking
the window.

Maybe it was silicone and soap that worked, but with the silicone after the
soap it went right in, and has stayed in leak free for 10 years so far (this
was on a friend's T2).  I last used this method on the rear window on my '85
three years ago after Dawn failed again.

There are cleaners for removing silicone before you paint, but any REAL
paint job would be sanded down or chemically stripped to metal anyway!

Stuart