More bad news...I was just informed that, during a 100-hour, the IO-360-L2A in my 172S read 20/80 on cylinders 1 and 2. The kicker? Cylinder #1 was replaced in February, about 300 hours ago, due to reading nearly no compression. #2 is likely from the overhaul, 1200 hours ago. The shop is evaluating right now, but I'm curious what could be causing repeated failures like this? What sorts of questions should I be asking? This is very frustrating...the parallel valve IO-360 is supposed to be bulletproof. EDIT: Another thing I should note, since this plane is a leaseback, it gets 100 hour inspections. At the last 100 hour, compressions were fine. Need to go figure out exactly how high, but it was high enough that no concern at all was noted, so I'm assuming over 65/80. Whatever happened, it didn't give any warning. Oil analysis was also clean.