I may be doing just that. But if I can find better it will cost me less money in the paint shop.
Can't speak to your question on this cab since it's been in a barn and hasn't seen a drop of water in the dozen years or so we have had it stored there we never drove the truck or came from but on my 85 yeah it did have a leak into the cab, but the source there was brittle and cracked out seam sealer that broke away from its mount. I have to re seam seal that one before I put the ac plenum box back in and the cowl back on. All below the roofline.
One other thing about the cab I have now was that when I loaded it up on my trailer I didn't get out of the driveway (long farm driveway) and the back window about fell out, I had to stop and grab it before it did so it didn't shatter.
Between then and getting it stripped and delivered to the paint shop I talked to the guy my kid got it from/ who did mention that the whole time he had the truck that can was pulled from, he had an issue keeping the back window in place while he owned and drove that truck. But by the time that guy had gotten the truck it was 20 years old already... It had been this other guys "high school ride"