It's supposed to be a dry fit. Pieces of RTV could break off and get stuck in a rad fin, plus some RTV doesn't cure hard. They're of course usually difficult to push in when dry, so I use water as a lubricant so there's no residue. Here’s the story I tell everyone, you'll already know a lot of this. Clean all contact surfaces, preferably followed with an alcohol wipe, regular solvent and soaps can leave an oily reside. You can roughen any shiny surfaces with sandpaper if you want. Put the rubber collar in first, some try to put them in together. What ever you do, don't use a hammer. I use a clamp to press them in with a wood block on the back side for protection so you don't risk cracking the plastic side tank, especially important for an old tank. If a tank should ever crack then I figure it was getting brittle and would soon start to fail in any case. I have LH where you press in a dummy plastic plug that has a slightly roughened surface to grip the rubber grommet (the plug is sometimes taped underneath when you buy a new rad). Regina has the t-stat and you have to use something like a socket over the spade terminals. For years I didn't bother to secure them figuring Volvo didn’t think they needed to. Mind you, to be safe, in my hotter turbo engine compartment I did go to the lower pressure black 240 rad cap, but that was mostly for the sake of protecting the heater valve and heater core. I'll take a blown plug any day over those. After a sudden rise in pressure caused by a leaking head gasket I did have a blow out in my other NA 940. Since then I'm a big believer in securing them. Many use nylon zip ties poked through the rad and around the side tank. Cheap dollar store ties won't last more than a year or so. Black UV ties like Volvo uses will last longer. I do two in a cross so that they can't slip off and one tie can fail before I notice it. I like your wire method better.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now