I've read a bit about it but I'm kinda on the fence about which to do. I absolutely need a working overdrive as I'll be highway commuting with this car, but for $40 vs $80 is not *that* huge of a difference. $40.00 seems high for a block-off plate and $80 seems cheap for a replacement solenoid. Seems I can get an aftermarket replacement for about $60.00.

Have people had much luck with junkyard solenoids? There are very few 240s at the local yards, but I see a lot of 740s and 940s - do those use the same part?

I am fairly sure it's not the relay. It audibly clicks and the light comes on. The OD is not intermittent at all. Admittedly, I've not done a voltage test yet... However, I took it on a 130 mile trip and it never even threatened to engage.