suggestions on sealing sashes

I have a large number of nice old double hung windows (morticed corners, some bubbles/ripples inthe glass) that I'm reluctant to replace with modern, tasteless windows. I've reglazed them, made sure the exterior storms are functioning, and weather stripped the sashes. The only place that seems to be a real issue is where the sashes meet. Anybody have any suggestions? the weather stripping seems temporary, since that area gets a lot of wear int he summer, and I've tried a few other techniques - masking tape, some kind of silicone caulk-like stuff, and the more putty like 'rope caulk.' None really seem ideal, (they all more or less work, but leave something behind) but I'm running out of ideas.

Thanks
Steve

What kind of weatherstrip did you use? The cheesy foam stuff?

I've used some small roundish rubber (some are felt) stripping that you can attach with brads and should last compared to foam.

I used the plastic V-strip against the rail that separates the sashes, and tried that along the intersection between the sashes. It's really just that seal where the sashlock is that seems to be an issue, but the V strip just doesn't adhere well enough over the long haul.

Steve