I've been faithfully scanning the BB almost daily since getting my '93 940 nearly 7 years ago, and can't recall any reports of Rex coil failures other than a few authoritatively phrased doomsday warnings such as:
"These tend to fail more often than the Bosch arrangement." and
"The coil pack is a notorious problem with these cars and other cars that use a similar arrangement." In another post, this same person stated, "In reality, the coil rarely fails."
So much for authority.

Here are some google searches you can try:
rex ignition coil site:brickboard.com
regina ignition coil site:brickboard.com [many confuse Rex & Regina]

Neither my '93 (172K miles) nor son's '92 (about 215K) have had a coil/power stage problem. But I did remove my coil once just to look at and clean the primary contacts. Pics below:




NOTE:One authority also said that poor coil/power stage grounding can cause problems. That warning prompted me to make This test.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.