Not sure exactly what you are talking about. For one thing, "240 2.3i 1986 – 1991" encompasses at least 3 different Biosch units not counting the oddballs used in the 50 states federal EPA cars (California cars). Of those 3 main ECUs two never fail. Never as in we don't see more than a post or two a year that might involve trouble with the ECU. If that.
For the '89 561 ECU, probably everyone regularly on the board is aware of its trouble. Not really a big deal, 2 minutes to swap ECUs and $30 (find your own upgrade 951) or $150 (buy one on Ebay when you need it) and you are good to go another decade. But the '89-on normally aspirated cars usually equipped with 561s, (some 951s have failed) are the only cars likely to suffer ECU failures.