I second the main seal as a place to look. But also look at the seal around the rear glass. I've had trouble there. Comes and goes.

Try putting silicone lubricant on all the seals. That may temporarily limber them up and close any gaps--if that stops the leak, you'll know it's a seal problem. Be careful not to get that stuff on the paint, however. I've applied it by saturating a "disposable cloth" towel and then wiping the rubber.

For the window seal, you could get a windshield sealant gun and do it right. But that's a lot of sealing to do without knowing whether that's even the problem area.

Then there are the license plate light housings. They have seals too, or the units may be coming loose. In heavy rain, water can wick into the tailgate and from there get past the main seal.

And...do you have any rust at the base of the rear quarter glass? Water can get in a hole there and go down into the body--even get into the rear seat wells from there.

Have you done a hose spray test?

Also--try hard to keep leaves and trash out of the outside air grille below the windshield. On the 240 there isn't any way to clean that out (my nominee for the worst design decision on the whole car), and if the drain holes in the rocker panels plug up, you get interior leaks or rust. There's a thread a few weeks back about cleaning out the rocker panels.

For what to do about freezing rain and no garage, my only suggestion is, move. Fla-Tex-Cal?

Doug