I have to agree with you that the seal was clearly not good enough! It is not however the rubber seal but the actual orifice! I repaired the edges as you did and didn't really think about changing the shape of my windows, you can imagine my horror when I found that each window orifice is not only a different size but is also a different shape I have had to have each window custom made so hopefully they will now seal a bit better!!
Our "new" Dormobile panel-van-conversion was fitted with incorrect seals (I think perhaps the ones Just Kampers sell). The seals were designed for 5mm glass and 5mm body, while the body is more like 1mm, if that. Water seems to get inside the seal channel on the bodywork side, runs down inside the seal channel to the bottom, and then sits rusting the edge of the window opening. Our van had lots of rusty drip marks on the inside, and quite a bit of water leaking in when it rained. I've sanded and scraped the rust around the edges of the opening back to mostly metal, treated with phosphoric acid rust converter, and painted with grey zinc primer, white primer, then white top coat (rattle cans from Halfords). I've bought new seals from Seals Direct, designed for 5mm glass and 1.6mm body (part number WR62). Plan to install this with a thin bead of black sealant (Tiger Seal polyurethane adhesive & sealant) in the channels, as recommended by Seals Direct. Hopefully the combination of tighter fit and sealant will mean no water can get in any more.
I've got two devon 6 pane jalousie windows for sale that im pretty sure came out of a panel van conversion. Need a clean up but glass is all good. Theyre in my for sale thread if you want to have a look
Update: The new WR62 seals are lovely, and fit very well. The window glass now sites much more in the same plane as the metal panel. The old seals, which had slots too wide for the thin metal, result in the glass sitting more inside the bodywork, presumably because the metal shifts to be diagonal in the slot. That leaves a nice gap for water to get in and run around, leading to quick rusting and leaks... The black PU sealant is sticky and messy, and gets everywhere if you put too much in the slot. Next time I'll put much less in the slot. I think it's still worthwhile to use, at least on the metal side of the seal, and especially if the metal edge is thinned and uneven from past rust.
Heritage apparently sell a channel insert that sits around the window edge and takes up the slack in the window rubber
