I hope that your diagnosis proves to be correct, no reason from my perspective it shouldn't be, but I notice that one very common problem usually goes unmentioned when these things are discussed. That being the Llambda Relay. I think that the 240 run throughout was so equiped, [but I could very well be mistaken since I focus on one of the earlier models], but when the relay does go bad the car goes into a 'limp-home' mode of sorts which is typified by a sudden power loss of about 40% or so, which can be accompanied by stuttering, and stalling etc... It is a very easy problem to diagnose IF you know what to look for, and moreover in the interest of preventative maintenance it is worth learning what to look for while the relay is functioning normally so that its failure will be easily noticed.

While the car is running (again I am assuming that the realy location is uniform for all models - which may not be the case - please correct me if I'm wrong) lift the hood and while facing the windshield listen for a very high pitched rapid clicking on the left side [it is a very apparant sound] that is a functioning Llambda relay. In the event that you experience loss of power, stuttering etc, you can very quickly determine if this is the problem if you lift the hood and that sound is absent.

Just a thought, it is a cheap fix, but unless you know what you are looking for, one easily overlooked, and a good opportunity for an inexperienced mechanic to replace everything but the kitchen sink without solving the problem.

Hope that is helpful.